DE102020212472A1 - Electrically heated catalytic converter - Google Patents

Abstract

The invention relates to an electrically heatable catalytic converter with at least one heating conductor, which is accommodated in a housing (11), with at least two electrical feedthroughs (19), by means of which the heating conductor can be electrically contacted through the housing (11), the heating conductor passing through a honeycomb body (10) through which air can flow in a main direction of flow is formed, which is formed from a layer stack (12) wound around a winding center (15) and formed from a plurality of foils stacked on top of one another, the winding center (15) being formed by at least two winding mandrels is, wherein the winding center (6, 15) is offset to the center of the layer stack (12).

Description

technical field

The invention relates to an electrically heatable catalytic converter with at least one heating conductor, which is accommodated in a housing, with at least two electrical feedthroughs, by means of which the heating conductor can be electrically contacted through the housing, the heating conductor being formed by a honeycomb body through which flow can take place in a main flow direction, which is formed from a layer stack wound around a winding center, which is formed from a plurality of foils stacked on top of one another.

State of the art

Electric heaters are used to heat the exhaust gas or the structures provided for treating the exhaust gases in the exhaust tract, such as honeycomb bodies of catalytic converters. As a result, faster heating can be achieved, which means that the so-called light-off temperature, from which the chemical conversion on a catalytic converter works to a sufficient extent, is reached earlier and thus the exhaust gas treatment is improved. This is particularly advantageous in situations after a cold start, which occurs in particular after the internal combustion engine has been idle for a long time.

The heating element, which is usually arranged inside the exhaust pipe or inside the housing of a catalytic converter, must be electrically contacted. Depending on the voltage applied, a single electrical contact may be sufficient or, at higher voltage levels, two individual electrical contacts must be provided in order to connect the heating element to the poles of a voltage source and thereby prevent short circuits.

Solutions are known in the prior art that provide two electrical feedthroughs for contacting the electrical conductor, which acts as a heating element. These are often offset by 180 degrees from one another along the circumference of the catalyst housing.

A particular disadvantage of the devices in the prior art is that such an offset arrangement leads to a maximum distance between the connection points for the positive pole and the negative pole of the voltage source. This makes it more difficult to lay and connect the electrical lines to the connection points. This is particularly disadvantageous with regard to the temperatures prevailing in the area of the exhaust line and the limited installation space available.

In addition, the probability of electromagnetic fields occurring is increased by conducting the two electrical poles separately from one another, especially at higher voltage levels. This can lead to unwanted and adverse effects.

Presentation of the invention, task, solution, advantages

It is therefore the object of the present invention to create an electrically heatable catalytic converter which is designed in an optimized manner with regard to the electrical contacting of the heating conductor.

The object with regard to the electrically heatable catalytic converter is achieved by an electrically heatable catalytic converter having the features of claim 1.

One exemplary embodiment of the invention relates to an electrically heatable catalytic converter with at least one heating conductor, which is accommodated in a housing, with at least two electrical feedthroughs, by means of which the heating conductor can be electrically contacted through the housing, the heating conductor being formed by a honeycomb body through which flow can take place in a main flow direction which is formed from a layer stack wound around a winding center, which is formed from a plurality of films stacked on top of one another, the winding center being formed by at least two winding mandrels, the winding center being arranged offset to the center of the layer stack.

The heating function is generated by applying an electrical voltage to the heating conductor. Using the ohmic resistance, heat is generated at the heating conductor. The heat conductor is preferably formed by a metallic honeycomb body which is arranged upstream or downstream of other honeycomb bodies in the flow direction of the exhaust gas.

The electrical bushings are used for electrical contacting of the heating conductor. In the case of higher voltages in particular, it is advisable to provide a separate bushing for each of the electrical poles of the voltage source and not to use the housing or the casing of the catalytic converter as ground. The electrical feedthroughs are therefore designed to be particularly temperature-resistant and ensure electrical insulation of the housing from the heating conductor.

The honeycomb body acting as a heat conductor has a plurality of channels through which a flow can flow from an inflow side of the honeycomb body to an outflow side of the honeycomb body along a main flow direction. The channels are formed between the mutually adjacent foils of the layer stack. By winding up the stack of layers, a disc-shaped honeycomb body is created, which can be adapted to different housing cross sections, such as round, oval or angular cross sections.

The foils that form the stack of layers can have corrugations or other structures which, in conjunction with smooth layers or partially corrugated layers, form the channels through which flow can take place. Honeycomb bodies formed from a stack of layers are well known.

The stack of layers is preferably placed between at least two winding mandrels and the stack of layers is wound up to form the disc-shaped honeycomb body by rotating the winding mandrels about an axis of rotation.

It is particularly advantageous if the stack of layers has a longitudinal extent and a transverse extent, the transverse extent coinciding with the main flow direction of the catalytic converter and being significantly shorter than the longitudinal extent.

The foils are preferably formed by strips which have a longitudinal extent which is significantly greater than their transverse extent. Since these are foils, the extension in the third dimension, the thickness, is very thin and thus significantly smaller than the extension in the transverse and longitudinal directions. The foils are stacked on top of each other, for example alternating a smooth layer and an at least partially structured layer.

The resulting stack of layers thus also has a significantly greater longitudinal extent than the transverse extent. The height of the layer stack is determined by the number and thickness of the individual foils. The transverse extent of the stack of layers is in the same direction as the main flow direction of the channels of the honeycomb body.

It is also advantageous if the winding center forms the fulcrum around which the stack of layers is wound up by the winding mandrels. The winding center is determined by the mandrels used and is preferably in the center of the mandrels. The pivot point around which the stack of layers is rotated is preferably exactly in the winding center. However, in special designs it can also be provided that the pivot point is arranged eccentrically to the winding center. The axis of rotation running through the pivot point is particularly preferably parallel to the main flow direction of the channels.

A preferred embodiment is characterized in that the winding center along the longitudinal extent of the stack of layers is offset by a defined distance from the center of the stack of layers in the longitudinal direction.

This is particularly advantageous for creating an asymmetrical cross-sectional area. The areas of the stack of layers that protrude beyond the winding center on the right and left are therefore not of the same length. By winding up the stack of layers that is not arranged centrally in the winding center, an asymmetrical cross section of the honeycomb body is produced, in particular the free ends of the stack of layers, which would be located at areas offset by 180 degrees along the circumferential direction if the stack of layers were arranged centrally in the winding center, are closer together when viewed in the circumferential direction . The two electrical feedthroughs can thus be arranged closer together, as a result of which the undesirable interference effects, such as the occurrence of electromagnetic fields, can be minimized.

The resulting asymmetry of the honeycomb body can be influenced by changing the position of the layer stack relative to the winding center. In particular, the position of the free ends can be influenced in this way. The position of the engagement points of the winding mandrels in the honeycomb body can also be influenced.

It is also preferable if the honeycomb body has an asymmetrical cross-sectional area. The cross-sectional area is preferably formed by the area of the inflow side or the outflow side, or a parallel shift to these. An asymmetrical cross-sectional area is characterized in particular by the non-symmetrical arrangement of the free ends of the layer stack, which act as contact points for the electrical feedthroughs. In addition, the position of the center of the honeycomb body and the center of the housing is not necessarily congruent. The center of the honeycomb body is offset in one or two directions relative to the center of the housing, viewed in each case in a cross section.

In addition, it is advantageous if the honeycomb body has an envelope running in the circumferential direction, which follows the inner contour of the housing.

The enveloping curve of the honeycomb body corresponds to a boundary line running in the circumferential direction around the honeycomb body, depressions in particular, such as those that occur, for example, in the region of the ends of the layer stack, being spanned by the enveloping curve. The smallest possible distance between the inner contour of the housing accommodating the honeycomb body and the envelope is preferred, which ensures the electrical insulation of the honeycomb body from the housing but at the same time keeps the free cross section between the housing and honeycomb body as minimal as possible. This is intended to prevent unwanted flow around the honeycomb body. In particular, no bypass channel should be formed, which would significantly worsen the heating of the exhaust gas.

Furthermore, it is advantageous if the distance between the envelope of the honeycomb body and the inner contour of the housing is essentially equidistant along the circumferential direction of the catalytic converter. A distance between the envelope curve and the inner contour that is as constant as possible is particularly preferred in order to enable the most uniform possible flow through the honeycomb body and thus a uniform heating of the exhaust gas.

It is also expedient if the honeycomb body has two free ends of the stack of layers, these being offset from one another by less than 180 degrees along the circumferential direction of the catalytic converter. By winding up the stack of layers, at least two free ends are created within the honeycomb body. These preferably serve to make electrical contact with the honeycomb body. The fact that the winding does not take place in the middle of the stack of layers creates an asymmetry which results in the free ends being arranged closer to one another along the circumferential direction. In the case of center winding, the free ends are, for example, 180 degrees apart along the circumferential direction. More preferably, the free ends are less than 90 degrees apart along the circumferential direction, more preferably less than 45 degrees. The distance can preferably be reduced up to 5 degrees along the circumferential direction.

Advantageous developments of the present invention are described in the dependent claims and in the following description of the figures.

character list

• 1 einen Querschnitt durch das Gehäuse und den Wabenkörper, wobei die freien Enden nah beieinander liegen und sich zwischen dem Wabenkörper und dem Gehäuse ein breiter Spalt ausbildet,
• 2 einen Querschnitt durch das Gehäuse und den Wabenkörper, wobei die freien Enden nahe beieinander liegen und das Wickelzentrum versetzt zur Mitte des Gehäuses angeordnet ist, und
• 3 einen Querschnitt mit einer Anordnung entsprechend 2, wobei hier auch die elektrischen Durchführungen zur Kontaktierung der freien Enden gezeigt sind.

The invention is explained in detail below using exemplary embodiments with reference to the drawings. In the drawings show:

• 1 a cross section through the housing and the honeycomb body, the free ends being close together and a wide gap being formed between the honeycomb body and the housing,
• 2 a cross-section through the housing and the honeycomb body with the free ends close together and the winding center offset from the center of the housing, and
• 3 a cross section with an arrangement accordingly 2 , whereby the electrical feedthroughs for contacting the free ends are also shown here.

Preferred embodiment of the invention

the 1 shows the housing 1 of a catalytic converter. The honeycomb body 2 , which is formed by a wound stack of layers 3 , is arranged in the housing 1 . The layer stack 3 has been wound up by means of two winding mandrels, not shown, which were positioned at positions 4, 5. These winding mandrels were rotated about the winding center 6 located between the positions 4, 5, as a result of which the layer stack 3 was wound up.

The stack of layers 3 was positioned in the center of the winding center, as a result of which the two free ends 7, 8 would actually be offset from one another by about 180 degrees in the circumferential direction after winding. One of the free ends 7 has been shortened mechanically, which has resulted in the free ends 7, 8 finally being close to one another.

It can be seen that a relatively large free area 9 is formed between the honeycomb body 2 or an envelope curve surrounding it in the circumferential direction and the inner contour of the housing 1, which acts as a bypass for the exhaust gas flow, as a result of which the flow through the channels of the honeycomb body 2 is significantly worsened will. This free area 9 has essentially been created by shortening the free end 7 .

the 1 shows a honeycomb body 2 produced in a conventional manner, in which the layer stack 3 was positioned centrally in the winding device. By shortening a free end 7, an improved arrangement of the free ends 7, 8 relative to one another has been achieved, but at the same time the free area 9 has been created as a flow bypass.

2 shows a honeycomb body 10 in a housing 11. In contrast to 1 the honeycomb body 10 was formed by winding up the layer stack 12 offset to the middle of the layer stack 12 achieved, whereby on the one hand the free ends 13, 14 are closer together, and on the other hand the winding center 15, which is positioned between the two winding mandrel positions 17, 18, is offset from the center 16 of the housing 11.

The free end 13 can also be shortened in order to position the two free ends even closer together. It is different from 1 In particular, it can be seen that the asymmetrical design of the honeycomb body 10 minimizes or completely avoids the emergence of a free area between the housing 11 and the honeycomb body 10 . The flow through the honeycomb body 10 is thus significantly improved.

the 3 shows a structure similar to 2 . Additionally are in 3 the two electrical feedthroughs 19, 20 are also shown, which serve to electrically contact the two free ends 13, 14 of the honeycomb body 10.

The different features of the individual exemplary embodiments can also be combined with one another. The exemplary embodiments 1 until 3 in particular have no restrictive character and serve to clarify the idea of the invention.

Claims (8)

Electrically heatable catalytic converter with at least one heating conductor, which is accommodated in a housing (11), with at least two electrical feedthroughs (19), by means of which the heating conductor can be electrically contacted through the housing (11), the heating conductor running through a main flow direction permeable honeycomb body (10), which is formed from a layer stack (12) wound around a winding center (15) and formed from a plurality of foils stacked on top of one another, characterized in that the winding center (15) is formed by at least two winding mandrels , wherein the winding center (6, 15) is offset from the center of the layer stack (12). Electrically heated catalytic converter claim 1 , characterized in that the layer stack (12) has a longitudinal extent and a transverse extent, wherein the transverse extent coincides with the main flow direction of the catalyst and is significantly shorter than the longitudinal extent. Electrically heatable catalytic converter according to one of the preceding claims, characterized in that the winding center (15) forms the fulcrum around which the layer stack (12) is wound up by the winding mandrels. Electrically heatable catalyst according to one of the preceding claims, characterized in that the winding center (15) along the longitudinal extension of the layer stack (12) is offset by a defined distance from the center of the layer stack (12) in the longitudinal direction. Electrically heatable catalyst according to one of the preceding claims, characterized in that the honeycomb body (10) has an asymmetrical cross-sectional area. Electrically heatable catalytic converter according to one of the preceding claims, characterized in that the honeycomb body (10) has an envelope curve which runs in the circumferential direction and which follows the inner contour of the housing (11). Electrically heatable catalytic converter according to one of the preceding claims, characterized in that the distance between the envelope of the honeycomb body (10) and the inner contour of the housing (11) is essentially equidistant along the circumferential direction of the catalytic converter. Electrically heatable catalytic converter according to one of the preceding claims, characterized in that the honeycomb body (10) has two free ends (13, 14) of the layer stack (12), these being offset from one another by less than 180 degrees along the circumferential direction of the catalytic converter.

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