Exhaust gas after-treatment arrangement and method for operating such an arrangement

Abstract

Exhaust gas after-treatment arrangement and method for operating an exhaust gas after-treatment arrangement

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an exhaust gas after-treatment arrangement (i.e., assembly) and to a method for operating an exhaust gas after-treatment arrangement, having an exhaust line and at least one exhaust gas after-treatment device, which has a honeycomb body forming a flow surface for the exhaust gas.

2. Related Art

Exhaust gas after-treatment devices of this kind having a honeycomb body are known as catalytic converters for exhaust gas after-treatment. In general, the catalytic converter has a casing, which, on the one hand, surrounds the honeycomb body and, on the other hand, is connected to the exhaust line. The operating temperature required for the catalytic reaction is usually provided by the exhaust gas, which releases some of its heat to the catalytic converter as it flows through the catalytic converter and thereby heats it up. In attempting to optimize the catalytic converter with respect to costs and necessary installation space, the diameter of the catalytic converter is designed for an exhaust gas flow that requires to be defined, which is between the maximum and minimum occurring exhaust gas flow. Here, it must be taken into account that, relative to the cross section, the exhaust gas flowing through the exhaust line has a higher temperature in the center than in the radially outer regions at the wall of the exhaust line. During the heating of the catalytic converter and owing to the construction thereof, this likewise leads to a higher temperature prevailing in the center than in the region of the casing. To avoid inadequate heating of the catalytic converter at low exhaust gas flows, which has a disadvantageous effect on the catalytic reaction, the catalytic converter cannot be dimensioned for the maximum occurring exhaust gas flows. This, in turn, has the disadvantage that a high backpressure arises at high exhaust gas flows. A higher backpressure leads to an unwanted reduction in engine power and to higher fuel consumption.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide an exhaust gas after-treatment arrangement and a method for operating an exhaust gas after-treatment arrangement that ensures adequate after-treatment of the exhaust gas both for maximum and for minimum exhaust gas flows, without excessively affecting engine power or consumption.

According to an aspect of the invention, the object may be achieved by the honeycomb body being a hollow cylinder having a central channel, that a movable element is provided, which is movable between two end positions, wherein in a first of the two end positions a larger cross section of the channel is exposed than in a second of the two end positions.

The arrangement of the element movable between two end positions makes it possible to adapt the exhaust gas after-treatment device, in particular a catalytic converter, to the respective operating conditions, in particular of the exhaust gas flow and of the temperature of the catalytic converter. At low exhaust gas flows, which correspondingly supply a low energy for heating up the catalytic converter, and/or at a low temperature of the catalytic converter, the movable element is moved into the region of the second end position. The cross section of the central channel in the honeycomb body, which allows free flow, is thus reduced. The inflowing exhaust gas is thus directed radially outward and flows through the actual honeycomb body with its catalyst matrix, which is an arrangement of a plurality of sheet metal layers. In respect of the cross section of the exhaust line, the design of the honeycomb body with an annular catalyst matrix and a central channel leads to a reduced volume of the catalyst matrix. This ensures adequate heating to allow the required exhaust gas after-treatment, even at low exhaust gas flows. At high exhaust gas flows, the movable element is moved in the direction of the first end position. By virtue of the central channel cross section exposed in this way, some of the exhaust gas can flow freely through the channel, while the rest of the exhaust gas flows through the catalyst matrix. Owing to the exposed cross section in the channel, an excessive backpressure in the exhaust line is avoided. This prevents a drop in engine power and a rise in fuel consumption.

When such an exhaust gas after-treatment device with a small catalyst volume is used, the compressible gas volume is furthermore reduced. If the exhaust gas after-treatment device is arranged upstream of a turbomachine, in particular an exhaust gas turbocharger, this improves the dynamic behavior and response of the turbomachine.

In an advantageous aspect, the first end position exposes at least 75% of the channel cross section. A fully open channel has the advantage of producing the least backpressure, even at high exhaust gas flows. Nevertheless, it can be advantageous under certain circumstances to define the end position for a smaller opening cross section of the channel. Particularly in the case of a round channel cross section, significantly larger changes in cross section are achieved in the case of a semi-open channel than in the edge regions of a closed or fully open channel, given the same paths of the movable element. This means that the effort involved in moving the element in the edge regions is high but that only small changes in cross section are achieved. To this extent, the effort involved in moving the movable element can be significantly reduced by defining the first end position in a range between 75% and 100%. Depending on the embodiment of the movable element, it is possible to save installation space by virtue of the shorter path over which the element has to move. These advantages are obtained in the same way for the second end position if this is defined in a range in which at least 75% of the channel cross section is closed.

It is particularly advantageous if the movement of the element takes place in a rotary manner. For this purpose, the element may preferably be configured as a flap, which is secured on a shaft. The channel cross section is opened or closed by the flap by rotating the shaft.

In another advantageous aspect, the movement of the element takes place in the form of a pivoting movement. For this purpose, the movable element is connected to a pivoting arm, which is moved around a pivoting axis. The advantage of such an embodiment consists in that the pivoting axis can be positioned in the region outside the main flow, thus ensuring that the channel cross section is not obstructed by the pivoting axis.

The pivoting axis can advantageously be arranged in the wall of the exhaust line, preferably perpendicularly to the axis of the exhaust line.

The movable element can be configured in the manner of a closure plug, wherein the movable element is adapted in terms of flow engineering in accordance with the position on the inlet or the outlet side. Advantageous basic shapes here are a spherical, conical, spherical cup or droplet shape.

According to another advantageous aspect, the movable element is moved in translation. The advantage consists in that, during a movement of this kind, the element can be moved away from the channel cross section, thus ensuring that the cross section is completely free, while a flap and the shaft connected thereto cover part of the channel cross section, even in the fully open state.

In the simplest case, the movable element is a slide, in particular a rigid slide.

In another aspect, the movable element is a flexible slide. A flexible slide is a rolling diaphragm or a slide consisting of a plurality of rigid component elements connected movably to one another, for example. Slides of this kind allow unilateral fixing of the slide in the region of the second end position, simplifying the guidance of the slide.

If the exhaust gas after-treatment device is arranged close to a bend in the exhaust line, another advantageous aspect consists in configuring the movable element as a slide that can be moved in translation, wherein the movement of the slide takes place along the axis of rotation of the exhaust gas after-treatment device. The bend in the exhaust line has the effect that the slide that can be moved in translation or an element moving said slide can be passed out of the exhaust line, thus enabling the drive for the slide to be arranged outside the exhaust line. Thus, the channel cross section is virtually unaffected since, owing to the bend in the exhaust line, the gas flow is deflected in any case and the effect of the slide or the element moving the slide on the gas flow is negligible in comparison. Here, the design of the movable element for closing can likewise be in the form of a closure plug and it can be optimized accordingly in terms of flow engineering.

For reliable operation with long-term stability, it has proven advantageous for the movable element to be held and/or guided in the honeycomb foody. Furthermore this does not increase the length of the exhaust gas after-treatment device, and therefore no additional installation space in the axial direction is necessary for the arrangement according to the invention.

According to another aspect, the exhaust gas after-treatment device according to the invention allows the use of an unmodified honeycomb body if the movable element is held and/or guided in the exhaust line. Here, the element is positioned in such a way relative to the honeycomb body that it is arranged directly with respect to the central channel. Among the factors in favor of this option is the fact that the channel does not necessarily have to be closed. Complex seals are not required. Moreover, reliable implementation of the connection between the element and the drive can be accomplished by the appropriate design of the relevant section of the exhaust line.

Particularly good introduction of the exhaust gas into the catalyst matrix is achieved if the movable element is arranged in the region of the inlet of the channel in the flow direction.

If the movable element is arranged between the regions of the inlet and outlet, no additional axial installation space is required.

On the other hand, arranging the movable element in the region of the outlet of the channel in the flow direction has the advantage that, when the cross section is closed, the exhaust gas flowing into the channel can contribute more to the heating of the catalyst matrix surrounding the channel by virtue of its longer dwell time.

In the simplest case, the movable element is driven by an electric motor. By virtue of the good suitability of an electric motor for open-loop and closed-loop control, the element can be moved reliably and precisely as a result. Moreover, this embodiment makes it possible to select any desired intermediate positions, thereby ensuring good adaptability of the exhaust gas after-treatment arrangement according to the invention to different operating conditions.

In another aspect, electrical connections for the electric motor and the control system may be dispensed with if the movable element is moved in accordance with pressure conditions by being connected to a connecting rod subjected to pressure and spring force.

If, with the channel cross section open, that portion of the exhaust gas flowing through the channel is so large that it should also be subjected to exhaust gas after-treatment, it has proven advantageous if a second exhaust gas after-treatment device is arranged downstream of the exhaust gas after-treatment device. Since that portion of the exhaust gas that flows through the central channel has a shorter dwell time in the first exhaust gas after-treatment device and can thus release less heat to the first exhaust gas after-treatment device. This leads to significantly quicker warming up of the second exhaust gas after-treatment device.

The second object of the invention may achieved by virtue of the fact that the movable element is moved in the direction of the second end position in the case of low exhaust gas flows and is moved in the direction of the first end position in the case of higher exhaust gas flows.

By this method, the cross section of the central channel is increased or reduced depending on the volume of the exhaust gas flow. That portion of the exhaust gas flow that is directed past the catalyst matrix in this way via the channel as a bypass prevents the occurrence of a backpressure, which would arise if an excess of exhaust gas flow were passed via the catalyst matrix.

The adaptation of the arrangement to a very wide variety of exhaust gas flows can be achieved in an advantageous manner if the movable element can be moved into intermediate positions between the two end positions.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail by way of a plurality of exemplary embodiments. In the figures:

FIG. 1 is a schematic illustration of an exhaust gas after-treatment arrangement;

FIG. 2 shows the exhaust gas after-treatment arrangement according to FIG. 1 in a different operating state;

FIG. 3 shows further arrangements of the movable element; and

FIGS. 4-7 show further embodiments of the movable element.

DETAILED DESCRIPTION OF THE PRESENTLY PREFERRED EMBODIMENTS

FIG. 1 shows a section of an exhaust line 1 in which a catalytic converter acting as an exhaust gas after-treatment device 2 is arranged. Another exhaust gas after-treatment device 3, which is likewise configured as a catalytic converter, is arranged downstream of catalytic converter 2. Catalytic converter 2 has a casing 4, which surrounds a honeycomb body 5. The honeycomb body 5 is formed by a plurality of sheet metal layers, which form a catalyst matrix 6 and is a flow surface for the exhaust gas, wherein a catalytic reaction takes place in the exhaust gas as it flows through the catalyst matrix 6. Along its longitudinal axis, the honeycomb body 5 has a central channel 7, through which exhaust gas can flow, bypassing the catalyst matrix 6. The main flow direction of the exhaust gas is indicated by an arrow. Situated at the inlet 8 of the channel 7 is a movable element 9, which blocks the inlet 8 in the illustration shown. The movable element is a flap 9, which is secured on a shaft 10. The shaft 10 is connected to the electric motor 11 acting as a drive, allowing the flap 9 to be rotated by activation of the electric motor 11. In the position shown, the flap 9 is in the second end position. The inflowing exhaust gas is directed almost completely onto the catalyst matrix 6 and flows through the catalyst matrix 6. The flap 9 is moved into this end position at low exhaust gas mass flows, at which the catalyst matrix 6 is sufficiently large to ensure that the exhaust gas flowing through builds up almost no disruptive backpressure.

In the illustration shown in FIG. 2, the flap 9 has been rotated through 90° by the electric motor 11 and thus moved into the first end position, as a result of which the maximum possible cross section of the channel 7 is exposed. The flap 9 adopts this alignment at maximum exhaust gas mass flows. Some of the exhaust gas can flow unhindered through the honeycomb body 5 via the channel 7 in a kind of bypass. Only that portion of the exhaust gas flow which flows radially outward in the exhaust line 1 impinges upon the catalyst matrix 6 and flows through the catalyst matrix 6. That portion of the exhaust gas, which flows through the channel 7 and is not subject to after-treatment impinges downstream upon a second catalytic converter 3, which does not have a bypass channel, with the result that the entire exhaust gas flow must flow through the catalyst matrix for after-treatment. Owing to the almost unhindered flow through the channel 7, this portion of the exhaust gas flow releases little heat to the honeycomb body 5. As a result, the exhaust gas contains significantly more heat than if it had flowed through the catalyst matrix 6. The heat carried further along in this way is released at the second catalytic converter 3 by this exhaust gas flow. As a result, the second catalytic converter 3 warms up more quickly and the catalytic reaction tor exhaust gas after-treatment starts more quickly.

FIG. 3 shows a further arrangement of the movable element 9 in the honeycomb body 5, in which no additional installation space is required for the exhaust gas after-treatment arrangement 12 according to the invention as compared with a conventional honeycomb body 5.

In the case of the arrangement of the movable element 9 in FIG. 4, this element is arranged at the outlet 13 of the channel 7. The mounting for the movable element 9 is situated in the exhaust line 1, which has a separate section 14 in this region. In the illustration shown, the channel 7 is closed, although “closed” should not be taken to involve gastight sealing. The low leakage rates are negligible but, in return, allow significantly simpler and thus economical arrangement of the exhaust gas after-treatment device 2 relative to the movable element 9. As in FIG. 1, the element 9 adopts this alignment at low exhaust gas mass flows. In this case, a large part of the exhaust gas initially flows into the channel 7 before the exhaust gas, which then flows in behind is directed into the catalyst matrix 6. Owing to its dwell time in the channel 7, the exhaust gas in the channel 7 brings about significantly quicker heating up of the honeycomb body 5.

FIG. 5 shows the honeycomb body 5 with a rigid slide 15. The slide 15 is connected to an electric motor 11 by a connecting rod 16. The electric motor 11 drives the rod 16, thus allowing the slide 15 to be moved perpendicularly to the longitudinal axis of the honeycomb body 5 through the translational movement of the slide. In the illustration shown, the slide 15 is in the first end position and exposes 80% of the cross section of the channel 7.

FIGS. 6 and 7 show further embodiments, wherein, in FIG. 6, the movable element 9 is connected to a pivoting arm 17, which can be pivoted about a pivoting axis 18. The pivoting axis 18 is connected as a shaft 10 to a drive 11. In order to influence the channel cross section and hence the gas flow as little as possible, the pivoting axis 18 is arranged on the wall of the exhaust line 1 and thus outside the main flow. To close the channel 7, the movable element s has a closure plug 19 in the form of a spherical cup. which is connected to the pivoting arm 17. In order to keep the effect on the flow cross section small, it is conceivable to enlarge the cross section of the exhaust line 1 such that the enlargement 20 at least partially accommodates the movable element 9 that can be pivoted away from the catalytic converter 2.

The movable element 9 in FIG. 7 likewise has a closure plug 19 in the form of a spherical cup, which closes the channel 7. In the region of the movable element, the exhaust line is curved, and therefore the slide 21, which is connected to the closure plug 19 in a manner that allows it to move in translation, is passed to the outside through the exhaust line if it is arranged as an extension of the axis of rotation of the catalytic converter 2. The slide 21 is moved by a drive (not shown), which is situated outside the exhaust line 1.

Thus, while there have been 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.

Claims

1-20. (canceled)

21. An exhaust gas after-treatment assembly comprising: an exhaust line (1); andat least a first exhaust gas after-treatment device (2) having a honeycomb body (5) forming a flow surface for the exhaust gas,wherein the honeycomb body (5) is a hollow cylinder having a central channel (7) having an inlet (7), a movable dement (9, 15) is arranged such that the movable element (9, 15) is movable between first and second end positions, wherein when the movable element (9, 15) is in the first end position a larger cross section of the channel (7) is exposed than when the movable element (9, 15) is in the second end position.

22. The exhaust gas after-treatment assembly as claimed in claim 21, wherein the first end position exposes at least 75% of the channel cross section.

23. The exhaust gas after-treatment assembly as claimed in claim 22, wherein the second end position closes at least 75% of the channel cross section.

24. The exhaust gas after-treatment assembly as claimed in claim 21, wherein the first end position exposes at least 75% of the channel cross section.

25. The exhaust gas after-treatment assembly as claimed in claim 21, wherein the movable element (9) is movable in a rotary manner.

26. The exhaust gas after-treatment assembly as claimed in claim 25, wherein the movable element is a rotatable flap (9).

27. The exhaust gas after-treatment assembly as claimed in claim 24, wherein the movable element (15) is movable in translation.

28. The exhaust gas after-treatment assembly as claimed in claim 27, wherein the movable element is a slide (15).

29. The exhaust gas after-treatment assembly as claimed in claim 27, wherein the movable element is a rigid slide (15).

30. The exhaust gas after-treatment assembly as claimed in claim 27, wherein the movable element is a flexible slide.

31. The exhaust gas after-treatment assembly as claimed is claim 27, wherein the movable element comprises a plurality of movable blades.

32. The exhaust gas after-treatment assembly as claimed in claim 21, wherein the movable element (9, 15) is held and/or guided in the honeycomb body (5).

33. The exhaust gas after-treatment assembly as claimed in claim 31, wherein

34. The exhaust gas after-treatment assembly as claimed in claim 21, wherein the movable element (9, 15) is arranged in a region of the inlet (8) of the channel (7) in the flow direction.

35. The exhaust gas after-treatment assembly as claimed in claim 33, wherein the movable element (9, 15) is arranged in the region of an outlet (13) of the channel (7) in the flow direction.

36. The exhaust gas after-treatment assembly as claimed in claim 21, further comprising an electric motor (11) configured to drive the movable element (9, 15).

37. The exhaust gas after-treatment assembly as claimed in claim 21, further comprising a connecting rod (16) that is subjected to pressure and a spring force and is connected to the movable element (9, 15).

38. The exhaust gas after-treatment assembly as claimed in claim 21, further comprising a second exhaust gas after-treatment device arranged downstream of the first exhaust gas after-treatment device.

39. A method for operating an exhaust gas after-treatment assembly as claimed in claim 21, comprising: moving the movable element toward the second end position in the case of low exhaust gas flows; andmoving the movable element toward the first end position in the case of higher exhaust gas flows.

40. The method as claimed in claim 29, wherein the movable element is movable into intermediate positions between the first and second end positions.