WO2000071863A1

WO2000071863A1 - Heating element for heating flowing gases

Info

Publication number: WO2000071863A1
Application number: PCT/EP2000/004539
Authority: WO
Inventors: Anton Mangold; Matthias Mangold
Original assignee: Oberland Mangold Gmbh
Priority date: 1999-05-20
Filing date: 2000-05-19
Publication date: 2000-11-30
Also published as: DE19923228A1; EP1179123A1

Abstract

The invention relates to a heating element for heating flowing gases. The heating element comprises a first flat component which is electrically conductive and which can be heated by conducting an electric current through the same. The inventive heating element also comprises a second flat component which is electrically non-conductive, whereby the components are arranged such that a series of layers is provided, and the components form flow paths for the gas to be heated. In addition, at least several layers of the series of layers of the first flat component are insulated from one another by the second flat component. A waste gas system comprises at least one heating element which is arranged upstream, in a direction of flow, from at least one filter. According to the inventive method for heating flowing gases, at least one heating element is operated in a temporally selective manner.

Description

Heating element for heating flowing gases

The invention relates to a heating element for heating flowing gases, having a first flat component which is electrically conductive and which can be heated by conducting an electric current, and a second flat component which is electrically insulating, the components being arranged such that a layer sequence is present, and the components form flow paths for the gas to be heated.

A generic heating element is known from DE 196 40 577 AI. It is an electrically heated catalytic converter with a laminated structure, which is formed from corrugated metal foils and flat metal foils. There are a plurality of successive layers of corrugated and flat metal foils. The flat metal foils and the corrugated metal foils are each insulated from one another by insulating layers. There are areas with a high electrical resistance, so that with an applied voltage and a resulting current flow there are areas with a greatly increased temperature. Because of this arrangement, a high temperature for starting catalytic reactions is generated even at a low electrical current. The heating arrangement described in the prior art deals with the catalytic conversion of exhaust gases. However, there are other reasons for heating an exhaust gas flow.

In diesel engines, for example, it is known to filter out the soot particles in the exhaust gas in a filter within the exhaust system. If the diesel engine is operated with a high load, the exhaust gases passing through the filter are at a high temperature and the soot particles collected by the filter are burned due to the high temperatures. As a result, the filter is seldom clogged because it has a quasi self-cleaning effect. However, the operation of a soot filter is problematic under operating conditions of the engine which result in comparatively low exhaust gas temperatures. The exhaust gas temperature is then no longer sufficient to provide the energy required for the combustion of the soot particles in the filter. It can therefore also be useful to heat the exhaust gas flow in exhaust systems for diesel engines.

The invention is therefore based on the objective of providing a simple and effective way of heating flowing gases, which is particularly useful in connection with particle filters.

This object is achieved with the features of claims 1, 14 and 17.

The heating element according to the invention builds on the prior art in that at least some layers of Layer sequence of the first flat component are isolated from one another by the second flat component. The heating element is considerably simplified in comparison to the heating element described in the prior art and is particularly suitable for operation in connection with a particle filter. Since the heating element of the present invention is primarily not used to initiate a catalytic reaction, it is not necessary to provide local high temperature zones. Rather, the flowing gas must be given an elevated temperature overall so that the soot particles sitting in a subsequent filter can be burned. It is therefore possible to achieve the desired result with a layer sequence consisting of only two components. In particular, local high-temperature areas can be dispensed with, which enables the heating element to be constructed in a simple manner.

It is particularly preferred if the first flat component has at least one metal foil. Using a metal foil as an electrically conductive component is particularly advantageous, since metal foils are easy to process and withstand the extreme conditions in an exhaust system particularly well.

The first two-dimensional component is preferably wave-shaped. Such a wave-like design allows a particularly good heating effect to be generated in a given volume. The flowing gas comes into contact with a large area of the heated first flat component.

The components are preferably arranged in a spiral around a line core, so that the layer sequence arises. The two poles of the voltage supply are thus applied on the one hand in the center of the spiral arrangement, ie on the line core and in the outer region of the spiral arrangement.

The layer sequence preferably has at least four layers. An arrangement of four layers has proven to be advantageous in operation with regard to the flow processes and the heating of the gas.

It is particularly preferred if the spiral arrangement is arranged in a tube. In this way, the flow volume for the gas to be heated is defined, and the layer arrangement is provided with sufficient stability.

It may be advantageous that the length of the tube is greater than the axial length of the spiral arrangement. If, for example, the pipe protrudes downstream over the heating element, further functional elements can be provided on the pipe.

In this context, it is particularly advantageous if the tube is designed as an inner tube of a filter element. This gives a robust construction with a one-piece support, both for the filter element and for the heating element.

It is particularly preferred if the insulating component is a film made of temperature-resistant, flexible material. Due to the flexibility of the film, the shape of the layer arrangement can be varied; there is also flexibility with regard to the operation of the Heating element is advantageous because, due to thermal and mechanical effects, deformations of the layer arrangement can sometimes occur.

It can also be advantageous if the insulating component has an inner support layer, preferably made of metal, and outer layers made of an insulating material arranged on both sides of the inner support layer. This construction provides a robust, temperature-resistant heating arrangement.

The insulating film is preferably a glass fiber-reinforced mica layer which is temperature-resistant up to 900 ° C. Such an embodiment offers advantageous flexibility with regard to the

Manufacturing and sufficient resilience during the

Operation of the heating element.

The heating power can preferably be changed by changing the resistance of the first component. Such a change in resistance can be brought about by lengthening, shortening and / or widening the first component. Furthermore, the length, the thickness and the corrugation of the preferably wavy electrical conductor can influence the resistance and thus the heating power. The choice of material is also a parameter for changing the heating output. When changing the resistance through geometric measures, care must be taken that the insulating layer is adapted accordingly.

It can also be advantageous that some layers of the layer sequence of the first flat component are not insulated from one another. For example, if there is a spiral shaped arrangement within a tube before, the outer area can be "short-circuited" by omitting an insulating layer, so that this does not contribute to the heating of the flowing gas. This can sometimes result in higher heating efficiency, since the radiation of the thermal energy introduced into the gas from the areas near the pipe wall is reduced.

In the exhaust system according to the invention, at least one heating element is arranged in the flow direction in front of at least one filter. There is therefore an association between a heating element and a filter, so that the solid particles in a filter can be burnt off in a targeted manner by operating a heating element.

It is particularly advantageous if several filters and heating elements are arranged in parallel. In this way, each filter element can be specifically charged with heated gas.

It is particularly advantageous if at least one pressure measuring point is arranged in front of at least one filter. The pressure upstream of the filter during the operation of the exhaust system can be used as a measure of the clogging of the filter. Consequently, by measuring the pressure at a pressure measuring point, it can be determined at which point in time the use of a heating element is necessary. The load state of the engine can also be taken into account.

In the method according to the invention for heating flowing gases, at least one heating element becomes selective over time operated. If, for example, a diesel engine is operated with a high load, the use of a heating element is sometimes not necessary or only rarely due to the already high exhaust gas temperatures. There will be more frequent clogging of the filter at low load, so more frequent heater operation is useful. In any case, selective operation avoids subjecting heating elements to unnecessary continuous operation and unnecessarily drawing power from the vehicle electrical system.

The method according to the invention is particularly advantageous if the pressure is measured upstream of the at least one filter and the at least one heating element is operated as a function of pressure and as a function of the load condition of the motor in question. Since the pressure upstream of the filter is largely dependent on the solids content already collected by the filter, the suitable time periods for the operation of a heating element can be determined by the pressure measurement.

A plurality of heating elements and a plurality of filters are preferably used in the method, one heating element being assigned to a filter in each case; at least one heating element is operated when the pressure exceeds a threshold pressure, and different heating elements or different groups of heating elements are operated in the event of successive threshold pressure violations. For the proper operation of the exhaust system, it is sometimes not necessary to always ignite all heating elements when there is an increase in pressure. Consequently, selective ignition is sufficient, which depends, for example, on a predetermined sequence. It is also conceivable to measure the pressure in the exhaust system depending on the location, so that in this way the "correct" heating element can be selected in order to achieve the greatest possible burning effect. The invention is based on the surprising finding that it is possible with a simple heating element to always operate an exhaust system under almost optimal conditions. It proves to be particularly advantageous to choose an arrangement within the exhaust system that enables selective and thus economical and ecological operation.

The invention will now be described by way of example with reference to the accompanying drawings based on a preferred embodiment.

Fig. La shows a plan view of an embodiment of a heating element according to the invention;

1b is a sectional view through the insulating component in a preferred embodiment;

Fig. 2 shows part of an embodiment of an exhaust system according to the invention with a heating element;

FIG. 3 is a view of the exhaust system according to FIG. 2 in the direction of view marked III;

Fig. 4 is a view of the heating element in the in

Fig. La marked IV marked viewing direction;

Figure 5 is a view of a heating element inserted into an elongated tube. A heating element 2 according to the invention is shown in FIG. The heating element 2 comprises a corrugated metal foil 4 which is wound spirally. The layers resulting from this spiral arrangement are insulated from one another by insulating layers 6. Through the arrangement of the components described, flow paths 8 are formed for a gas to be heated. The layers are wound around a line core 10. The entire spiral arrangement is arranged within a tube 12. To heat the heating element, an electrical voltage is applied to the line core 10 and in the outer region to the metal foil 4. The electrical connection in the outer region of the spiral arrangement is preferably made by direct contacting of the tube 12. The heating element 2 is centrally supported by the line core 10 and thus stabilized. The voltage supply to the line core 10 takes place via a feed line 20, which is led through the pipe 12 through a, preferably ceramic, insulation 22 to the outside.

1b shows a section through the insulating component 6 in a preferred embodiment of the present invention. The insulating component 6 consists of three layers 6a, 6b, 6c, the middle layer 6b preferably being a metal layer, while the outer layers 6a, 6c are insulating.

Fig. 2 shows part of an exhaust system. A filter 16 is arranged in an exhaust pipe 14. The particle-laden gas flowing through the exhaust pipe flows into the filter 16 in an end region. The cleaned gas subsequently leaves the inner region of the filter 16 through the perforated outer region of the filter 16 which is provided with a filter medium. Flow paths are indicated by arrows as an example. The filter 16 shown is preceded by a heating element 2 so that the exhaust gas can be heated. A plurality of filters 16 are preferably arranged in the exhaust pipe 14. In front of the filters 16 there is a pressure measuring point 18, at which the pressure inside the exhaust pipe 14 can be determined. The pressure measuring point 18 can be realized, for example, by a tube leading to the outside of a pressure sensor. The more dirty the filters 16 are, the higher the pressure which is determined via the pressure measuring point 18. The operation of a heating element 2 can thus be made dependent on the pressure which is determined at the pressure measuring point 18. As a result, the heating element 2 is only operated if this is actually necessary. In an arrangement with a plurality of filters 16 and a plurality of heating elements 2, the heating elements 2 are also ignited as a function of pressure, but selectively and preferably in a predetermined sequence. The load state of the vehicle can be used as a further parameter for the selective ignition.

Fig. 3 shows the exhaust pipe 14 in the viewing direction marked III in Fig. 2. Several filters 16, 16 'can be seen, it being entirely possible to use different filters with regard to the geometric arrangement or also with regard to the filter material. In the present example, a central heating element 2 is provided, which serves to heat the gas for the cleaning of all filters 16, 16 '. FIG. 4 shows a heating element 2 inserted into a tube 12. Here, the electrical feed 20 to the line core 12 is also shown, which is led into the outer region of the tube 12 via a ceramic insulation 22.

5 shows a heating element 2 which is inserted into an elongated tube 12. The winding of the heating element 2 is pushed onto a constriction in the rear part of the tube 12. This is sufficient stabilization of the heating element 2 against slipping. The extended part of the tube 12 is provided with holes 24 so that gases flowing through the tube 12 can pass through the holes 24 to the outside. The actual filter medium is preferably attached to the outer area of the perforated tube part.

The features of the invention disclosed in the above description, in the drawings and in the claims can be essential for realizing the invention both individually and in any combination.

Claims

EXPECTATIONS:

1. heating element (2) for heating flowing gases, with

- A first flat component (4) which is electrically conductive and heatable by conducting an electrical current, and

- A second flat component (6), which is electrically insulating, wherein

- The components (4, 6) are arranged so that a layer sequence is present, and

- The components form flow paths (8) for the gas to be heated, thereby ensuring that at least some layers of the layer sequence of the first flat component (4) are insulated from one another by the second flat component (6).

2. Heating element according to claim 1, characterized in that the first flat component (4) has at least one metal foil (4).

3. Heating element according to claim 1 or 2, characterized in that the first flat component (4) is wave-shaped.

4. Heating element according to one of the preceding claims, characterized in that the components (4, 6) are arranged spirally around a line core (10), so that the layer sequence is formed.

5. Heating element according to one of the preceding claims, characterized in that the layer sequence has at least four layers.

6. Heating element according to claim 5, characterized in that the spiral arrangement is arranged in a tube (12).

7. Heating element according to claim 6, characterized in that the length of the tube (12) is greater than the axial length of the spiral arrangement.

8. Heating element according to claim 7, characterized in that the tube (12) is designed as an inner tube of a filter element.

9. Heating element according to one of the preceding claims, characterized in that the insulating component (6) is a film made of temperature-resistant, flexible material.

10. Heating element according to one of the preceding claims, characterized in that the insulating component has an inner support layer, preferably made of metal, and outer layers of an insulating material arranged on both sides of the inner support layer.

11. Heating element according to claim 8, characterized in that the insulating film (6) is a glass fiber-reinforced o mica layer which is temperature-resistant up to 900 ° C.

12. Heating element according to one of the preceding claims, characterized in that the heating power can be changed by changing the resistance of the first component (4).

13. Heating element according to one of the preceding claims, characterized in that some layers of the layer sequence of the first flat component (4) are not insulated from one another.

14. Exhaust system, in particular with a heating element according to one of claims 1 to 13, characterized in that at least one heating element (2) is arranged upstream of at least one filter (16) in the flow direction.

15. Exhaust system according to claim 14, characterized in that a plurality of filters (16) and heating elements (2) are arranged in parallel.

16. Exhaust system according to claim 14 or 15, characterized in that at least one pressure measuring point (18) is arranged in front of at least one filter (2).

17. A method for heating flowing gases, in particular with a heating element according to one of claims 1 to 13 in an exhaust system according to one of claims 14 to 16, in which at least one heating element (2) is operated selectively in time.

18. The method according to claim 17, wherein the pressure in front of the at least one filter (16) is measured and the at least one heating element (2) is operated in a pressure-dependent manner and in dependence on the load state of the motor in question.

19. The method according to any one of claims 17 or 18, in which

a plurality of heating elements (2) and a plurality of filters (16) are used, one heating element (2) being assigned to one filter (16),

- At least one heating element (2) is operated when the pressure exceeds a threshold pressure, and

- Different heating elements (2) or different groups of heating elements (2) are operated when successive threshold pressure violations.