SE540312C2

SE540312C2 - A device for controlling the flow of exhaust gas and a vehicle including such a device

Info

Publication number: SE540312C2
Application number: SE1550061A
Authority: SE
Inventors: Karlsson Jan
Original assignee: Scania Cv Ab
Priority date: 2015-01-23
Filing date: 2015-01-23
Publication date: 2018-06-12
Also published as: SE1550061A1; DE102016000442A1

Description

A device for controlling flow of exhaust gas and a vehicle comprising such a device Technical field On a general level, the present invention relates to a device for controlling flow of exhaust gas.

Background EU-legislation as regards emission of the exhaust gas generated by an internal combustion engine is normally tightened each 4-6 years. Historically, reductions in the emission of exhaust gas have been achieved through various measures, e.g. by means of filters or through improved management of nitrogen oxides produced during combustion.

Controlling the flow of exhaust gas, in particular its velocity profile, may also contribute in reducing the emission of exhaust gas. More specifically, a more even flow of exhaust gas upstream of a catalyst is beneficial for the performance of the catalyst itself. US20030159414 discloses a dual chamber structure that defocuses centralized exhaust gas flow upstream of a catalytic element and smooths out the flow profile of the gas stream across such element.

Purpose of the structure is to prevent push-out, i.e. deformation of the catalyst or filter element due to influx of the concentrated high velocity exhaust gas. Further purpose of US20030159414 is to reduce pressure drop in the exhaust gas system.

The disclosed dual chamber structure is partitioned by means of a perforated plate with circular, rather evenly distributed perforations. Circular, small-diameter perforations, such as those belonging to the structure at hand, are prone to clogging caused by crystallization.

On this background and in order to alleviate at least some of the drawbacks associated with the current art, an objective of the present invention is to provide a device that evens out the flow of the exhaust gas flowing towards the catalyst while avoiding the risk of crystallisation.

Summary In a first aspect of the present invention, the above stated objective is achieved by means of the device for controlling flow of exhaust gas generated by an internal combustion engine of a vehicle according to the independent claim.

Accordingly, the device is positioned upstream of a catalyst of the vehicle and it comprises a first chamber arranged to receive the generated exhaust gas via an exhaust gas inlet and a second chamber arranged to discharge the exhaust gas towards the catalyst via an exhaust gas outlet. The first and the second chambers are so arranged that a common interface is created, said interface being pervious to exhaust gas such that the exhaust gas may flow from the first to the second chamber and the interface comprises a plurality of parallel elongate apertures.

In the following, positive effects and advantages of the invention at hand are presented with reference to the first aspect of the invention.

The first chamber reduces turbulence of the incoming exhaust gas stream. Due to a pressure difference between the first and the second chambers, the exhaust gas subsequently passes through the apertures of the interface and into the second chamber. Its turbulence is hereby reduced and its flow is more uniform. This has several beneficial effects for the operation of the catalyst. More particularly, evening out of the flow permits more efficient catalytic process. This entails either a deployment of a smaller catalyst or a performance increase.

Moreover, improved catalytic process opens for a more efficient system for aftertreatment of the exhaust gas.

Furthermore, by physically separating the chambers by means of the interface, a favorable location for obtaining reductant is created. In the related context, crystallization of the obtained reductant is avoided due to the elongate shape of the plurality of apertures belonging to the interface.

A second aspect of the present invention relates to a vehicle comprising the claimed device for controlling flow of exhaust gas generated by an internal combustion engine.

Different embodiments of the invention are disclosed in the dependent claims and in the detailed description.

Brief description of the drawings Fig. 1 is a schematical view from above of a vehicle.

Fig. 2 is a contextual, schematical view of a part of an exhaust system of a vehicle comprising a device according to one embodiment of the present invention.

Fig. 3 is a first perspective view of a device according to an embodiment of the present invention.

Fig. 4 is a second perspective view of a device according to the same embodiment of the present invention.

Further advantages and features of embodiments will become apparent when reading the following detailed description in conjunction with the drawings.

Detailed description The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like reference signs refer to like elements.

Fig. 1 is a schematical view from above of a vehicle 1. The shown vehicle 1 is a truck or a trailer-hauling tractor having a chassis 9 and a front pair of wheels 10A and a rear pair of wheels 10B. The shown vehicle 1 is only an example, why the vehicle of the present invention may also be realized as a bus or even as a passenger car. A driver’s cab 7 is positioned far forward on the vehicle 1. A control unit 19, located below the driver’s cab 7, controls the operation state of an internal combustion engine 4 in accordance with the operating condition of the combustion engine 4 and/or driver inputs. Exhaust gases generated during the combustion process are channeled into an exhaust system 11. Accordingly and as schematically shown in Fig. 1, the combustion engine 4 is in fluid communication with the exhaust system 11. Operation of the exhaust system 11 is normally also controlled by the control unit 19.

Fig. 2 is a contextual, schematical view of a part of an exhaust system 11 of a vehicle 1 shown in Fig. 1. The vehicle comprises a device 10 according to one embodiment of the present invention. The inventive device 10 for controlling flow of exhaust gas is positioned in a channel 12 for exhaust gas discharged from a combustion engine 4. In this context and as is known to the one skilled in the art, flow of the discharged exhaust gas is predominantly turbulent. Moreover, the exhaust gas holds a temperature of approximately 450 - 700 °C.

The device 10 is located downstream of the engine 4 and upstream of a catalyst 17. The device 10 will be more thoroughly discussed in connection with Figs. 3 and 4. A unit 13 for dosing diesel exhaust fluid, in Europe commonly referred to as AdBlue®, into the stream of the exhaust gas is located intermediate the engine 4 and the device 10. Once the exhaust fluid is introduced into the hot stream, the aqueous fraction of the fluid is vaporized. The remaining compound is urea (reductant) that subsequently is vaporized. Product of this hydrolysis reaction is ammonia that at the catalyst 17 reduces levels of nitrogen oxides present in the exhaust gas.

The exhaust system 11 further comprises a control unit 19. Various sensors, such as exhaust gas temperature sensors and pressure sensors (not shown), are connected to the control unit 19. Output signals from these sensors are input to the control unit 19. As visualized in Fig. 2, the control unit 19 controls the operation state of the unit 13 for dosing exhaust fluid and the catalyst 17. This is done in accordance with the operating condition of the engine 4, the unit 13 and the catalyst 17 and/or sensor inputs. To this purpose, the control unit 19 typically has a processing unit 29 and a memory unit 39 connected to the processing unit 29. The processing unit 29 may comprise one or several CPUs (CPU - Central Processing Unit). The memory unit 39 could be of the non-volatile kind, e.g. a flash memory, or a RAM-memory (RAM - Random Access Memory).

Fig. 3 is a first perspective view of a device 10 according to an embodiment of the present invention. Accordingly, the device 10 suitable for controlling flow of exhaust gas generated by an internal combustion engine (shown in Figs. 1 and 2) is shown. The device 10 comprises a first chamber 33 arranged to receive the generated exhaust gas via an exhaust gas inlet 30, a second chamber 36 being arranged to discharge the exhaust gas towards a catalyst (shown in Fig. 2) via an exhaust gas outlet 39. The device at hand is typically made in a highly resistive metal, such as steel.

Fig. 4 is a second perspective view of a device 10 according to the embodiment shown in Fig. 3. Here, flow direction of the exhaust gas is denoted by arrows. As it may be seen, the first 33 and the second 36 chambers are so arranged that a common interface 35 is created, said interface 35 being pervious to exhaust gas such that the exhaust gas may flow from the first 33 to the second 36 chamber. Moreover, the interface 35 comprises a plurality of parallel elongate apertures 37. By physically separating the chambers 33, 36 by means of the interface 35, a favorable location for obtaining urea is created. In the related context, crystallization of the obtained urea is at least significantly reduced due to the elongate shape of the plurality of apertures 37 belonging to the interface 35.

The first chamber 33 reduces turbulence of the incoming exhaust gas stream. Due to a pressure difference between the first and the second chambers 33, 36, the exhaust gas subsequently passes through the apertures 37 of the interface 35 and into the second chamber 36. The turbulence of the gas is hereby reduced and its flow becomes more uniform. This permits more efficient catalytic process, resulting in either a deployment of a smaller catalyst or a performance increase. Furthermore, improved catalytic process opens for a more efficient system for aftertreatment of the exhaust gas.

As shown in Fig. 4, the flow direction of the exhaust gas at an exhaust gas inlet 30 is substantially perpendicular to the flow direction of the exhaust gas at an exhaust gas outlet 39. Advantageously, a more compact device 10 is hereby obtained. Moreover and as shown in Fig. 4, the interface 35 may be tapered towards the exhaust gas inlet 33. This means that the area available for gas to permeate from the first 33 to the second 36 chamber gradually increases. This also entails a deceleration of the exhaust gas and a more calm gas flow. In consequence, passage of the exhaust gas from the first 33 to the second 36 chamber is facilitated.

In the embodiment shown in Figs. 3 and 4, the interface 35 is convex in shape and so oriented that it curves towards the second chamber 36. Hereby, a structural stiffness of the device 10 is improved. This contributes to an increased eigenfrequency of the device 10. Furthermore, the convex shape paired with the above orientation entails a minor volume increase of the first chamber 33, when compared to a fully flat interface. In this context and considering the scarcity of space on a modern vehicle, even minor improvements are of importance. As inferable from Figs. 3 and 4, the first chamber 33 of the device 10 is smaller than the second chamber 36. This abates the flow of the exhaust gases and reduces occurrence of eddies and vortices. Stream of exhaust gas that has been modified in this manner is easier to guide through the device 10 and towards the catalyst.

An edge of material surrounding each of the apertures 35 is provided with a flange (not shown) extending towards the second chamber 36. These flanges typically have rough surfaces. Orientation of the flange is of importance since a rough surface provides a good ground for formation of urea deposits. In this context and with reference to Fig. 2, it has been established that most of the conversion of the exhaust fluid to urea takes place at the interface of the first 33 and the second 36 chambers.

In one embodiment (not shown), the first and the second chambers are both substantially disk-shaped. In a thereto related embodiment, the second chamber 36 has a diameter that equals diameter of a pipe 44 connected with the exhaust gas outlet 39 and leading to the catalyst (shown in Fig. 2). These features confer better control of the flow through reduced pressure losses in the device 10 and thereto associated piping.

In one embodiment, the ratio of the total area of the apertures 37 to the area of said interface 35 is below 0.7. Here and as is known to the one skilled in the art, the term total area of the apertures may be interchanged with the term open frontal area (OFA).

The device 10 may be part of a silencer of a vehicle. This configuration is particularly suitable for commercial vehicles, such as trucks. When the inventive device is employed in a passenger car, the device 10 is typically placed elsewhere.

In the drawings and specification, there have been disclosed typical preferred embodiments of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation, the scope of the invention being set forth in the following claims.

Claims

1. A device (10) for controlling flow of exhaust gas generated by an internal combustion engine (4) of a vehicle (1), said device (10) being arranged to be positioned upstream of a catalyst (17) of the vehicle (1), wherein the device (10) comprises: a first chamber (33) arranged to receive the generated exhaust gas via an exhaust gas inlet (30), a second chamber (36) being arranged to discharge the exhaust gas towards the catalyst via an exhaust gas outlet (39), the first (33) and the second (36) chambers are so arranged that a common interface (35) is created, said interface (35) being pervious to exhaust gas such that the exhaust gas may flow from the first (33) to the second (36) chamber, wherein said interface (35) comprises a plurality of parallel elongate apertures (37), characterized in that the flow direction of the exhaust gas at the exhaust gas inlet (30) is substantially perpendicular to the flow direction of the exhaust gas at the exhaust gas outlet (39) and in that said interface (35) is tapered towards the exhaust gas inlet (30).

2. A device (10) according to claim 1 , wherein an edge of material surrounding at least one of the apertures (37) is provided with a flange extending towards the second chamber (36).

3. A device (10) according to any of preceding claims, wherein the first (33) and/or the second (36) chambers are substantially disk-shaped.

4. A device (10) according to any of preceding claims, wherein the second chamber (36) is substantially disk-shaped and has a diameter that equals diameter of a pipe (44) connected with the exhaust gas outlet (39).

5. A device (10) according to any of preceding claims, wherein said interface (35) is convex in shape and so oriented that it curves towards the second chamber (36).

6. A device (10) according to any of preceding claims, wherein the first chamber (33) is smaller than the second chamber (36).

7. A device (10) according to any of preceding claims, wherein the ratio of the total area of the apertures (37) to the area of said interface (35) is below 0.7.

8. A device (10) according to any of preceding claims, wherein said device (10) is part of a silencer of the vehicle (1).

9. A vehicle (1) comprising a device (10) according to any of preceding claims.