Patent Application
20110099990
The present invention relates to an assembly for cooling an exhaust gas stream.
The exhaust gas standards enacted by the European Union provide for a gradual reduction in the soot particles produced by diesel engines and discharged into the environment with the engine exhaust gas. Soot particle discharge is restricted by using soot particle filters, as a rule with “wall-flow filters”, in which the engine exhaust gas passes through a porous filter wall of a ceramic or metallic material. In so doing, the soot particles contained in the engine exhaust gas become deposited both on the surface of and also inside the filter wall, such that the exhaust gas back-pressure increases as the degree of clogging of the filter wall increases. To regenerate the soot particle filter, the deposited soot particles are therefore burned off at regular intervals, for which purpose the temperature of the engine exhaust gas is increased from time to time to temperatures of over 600° C., for example using an oxidation catalytic converter connected upstream of the soot particle filter. During the regeneration phases of the soot particle filter correspondingly high exhaust gas temperatures may occur at the exhaust tail pipe of the exhaust gas system, which may possibly constitute a hazard for nearby vehicle components, objects or people.
Against this background, WO 2008/060559 A2 discloses a device for reducing the exhaust gas temperature at an exhaust tail pipe. The device, which may be fitted to the exhaust tail pipe by means of a clip or clamp, comprises a nozzle, which is fitted by means of a plurality of radially arranged holding struts in such a way on an adjoining diverter housing that, on passage of the exhaust gas stream, a partial vacuum for drawing in cooler ambient air may be produced in an inlet formed between the nozzle and the diverter housing. However, the shape of the nozzle or of the diverter housing, which shape tapers in the passage direction of the exhaust gas stream, leads to an undesired increase in the exhaust gas back-pressure in the exhaust gas system.
Accordingly, an object of this invention is to provide an exhaust gas cooling assembly which prevents an undesired increase in the exhaust gas back-pressure during regeneration phases of the soot particle filter.
This and other objects are achieved by the present invention, wherein an assembly for cooling an exhaust gas stream includes an outlet nozzle exposed to the exhaust gas stream. The outlet nozzle projects into an open end of an adjacent exhaust gas pipe so that a reduced pressure relative to the surrounding environment is produced in a suction region between the outlet nozzle and the exhaust gas pipe due to the flow of the exhaust gas stream. Furthermore, an adjusting device is provided for varying the flow cross section of the outlet nozzle.
More precisely, the reduced pressure is produced by the Venturi principle, the outlet nozzle extending into the open end of the exhaust gas pipe and producing a reduced pressure in the suction region as a function of the flow cross section. The ambient air drawn into the exhaust gas pipe due to the reduced pressure leads in the process, depending on the temperature thereof, to corresponding cooling of the exhaust gas stream.
Since the addition of cooler ambient air is needed only during the regeneration phases of the soot particle filter, during the other operating phases of the soot particle filter the flow cross section of the outlet nozzle may be enlarged by the adjusting device such that the exhaust gas stream can pass through unhindered. In this way, an undesired increase in the exhaust gas back-pressure may be restricted to the regeneration phases of the soot particle filter.
The assembly has a particularly simple structure which fits compactly in the region of the soot particle filter inside an engine compartment of a diesel-engine powered motor vehicle, such as an agricultural utility vehicle. Cooling of the diesel engine is conventionally achieved by a high temperature heat exchanger arranged in the engine compartment of the motor vehicle, which heat exchanger is a component of a liquid cooling circuit connected with the diesel engine. The high temperature heat exchanger is exposed to cooling air by a fan unit. Cooling air is drawn from the surrounding environment by way of a radiator grille and downstream filter inserts. Since the air conveyed in this way into the engine compartment is largely free of contaminants, undesired clogging of the suction region formed between the outlet nozzle and the exhaust gas pipe is reliably avoided. In addition, the compression of the air located in the engine compartment by the fan unit, leads to an increased volumetric flow rate in the suction region and thus to more efficient cooling of the exhaust gas stream.
The flow cross section of the outlet nozzle is preferably varied as a function of the exhaust gas temperature. In particular, provision may be made for the flow cross section to be enlarged by the adjusting device in the case of exhaust gas temperatures typically arising during a regeneration phase of the soot particle filter.
The outlet nozzle may comprise a plurality of flexible fins for varying the flow cross section. The fins take the form for example of finger-shaped baffle plates, which are one-piece components of a fastening strip mountable on an outlet connector of the soot particle filter, the baffle plates projecting towards the exhaust gas stream when fitted. The outlet connector is in particular a fixed component of a filter housing surrounded by the soot particle filter and is welded or otherwise firmly connected thereto.
The fins are preferably bimetallic elements, which assume a curvature which reduces the flow cross section of the outlet nozzle as the exhaust gas temperature increases. In other words, the bimetallic elements constitute an adjusting device for temperature-dependent variation of the flow cross section of the outlet nozzle. The structure of such bimetallic elements is known in principle. Accordingly, they consist of a metal strip, which comprises two joined-together metal layers with different coefficients of longitudinal expansion.
The fins are preferably configured so that they rest against the open end of the exhaust gas pipe when the exhaust gas temperature is below a predetermined threshold value. In this case the fins adopt a fully open position. The threshold value is preset such that it is below the exhaust gas temperatures in the range of from 400 to 600° C. typically occurring during the regeneration phase of the soot particle filter.
A limiting member is provided at the open end of the exhaust gas pipe for the fins to rest on. The limiting members form of a stop lip extending around the inside of the open end of the exhaust gas pipe. The stop lip forms a flange at the open end of the exhaust gas pipe. A heat-resistant seal in the form of a braided glass or ceramic fibre cord may additionally be introduced into the flange.
Moreover, the fins may be arranged overlapping in the manner of a diaphragm in the circumferential direction of the outlet nozzle. The overlap reliably prevents an undesired release of exhaust gases in the region of the outlet nozzle.
Preferably, the exhaust gas pipe is surrounded at least in places by a touch guard. The touch guard takes the form in particular of a tubular cover, which is fitted along the outside of the exhaust gas pipe by means of a plurality of spacers. To prevent overheating of the exhaust gas pipe, the tubular cover may include a plurality of openings at least in the region of an exhaust tail pipe, which allow circulation of the air present between the exhaust gas pipe and the tubular cover.
Referring to
To cool the exhaust gas stream 18 emerging from the soot particle filter 14 and heated during the regeneration phase, the assembly 20 includes an outlet connector 22 formed on the soot particle filter 14 for conveying out the filtered exhaust gas stream 18. An outlet nozzle 24 fitted on the outlet connector 22 and exposed to the exhaust gas stream 18 projects into an open end 26 of an adjacent exhaust gas pipe 28 so that a reduced pressure relative to the surrounding environment 32 is produced in a suction region 30 between the outlet nozzle 24 and the exhaust gas pipe 28 by the flow of the exhaust gas stream 18, as best seen in
More precisely, the reduced pressure is produced by the Venturi principle, the outlet nozzle 24 extending into the open end 26 of the exhaust gas pipe 28 and producing a reduced pressure in the suction region 30 as a function of the respective flow cross section. Ambient air 34 is drawn into the exhaust gas pipe 28 due to the reduced pressure leads in the process, depending on the temperature thereof, to cool the exhaust gas stream 18.
Furthermore, the outlet nozzle 24 includes a plurality of flexible fins 36 for varying the flow cross section. The fins are arranged overlapping in the manner of a diaphragm in the circumferential direction of the outlet nozzle 24. The fins 36 take the form of finger-shaped baffle plates, which are one-piece components of a fastening strip 40 mounted on an outlet connector 22 by means of a clamping screw 38. The baffle plates project towards the exhaust gas stream 18 when fitted. The outlet connector 22 is a fixed component of a filter housing 42 surrounded by the soot particle filter 14 and is welded or otherwise firmly connected thereto.
The fins 36 are bimetallic elements, which assume a curvature which reduces the flow cross section of the outlet nozzle 24 as the exhaust gas temperature increases. In other words, the bimetallic elements constitute an adjusting device 44 for varying the flow cross section of the outlet nozzle 24 as a function of the exhaust gas temperature.
Moreover, the fins 36 are configured so that they rest against the open end 26 of the exhaust gas pipe 28 when the exhaust gas temperature is below a predetermined threshold value. In this case, the fins 36 adopt a completely open position, to allow the exhaust gas stream 18 to pass through unhindered, as best seen in
At the open end 26 of the exhaust gas pipe 28 a limiting member 46 is provided for the fins 36 to rest on. The limiting member 46 takes the form of a stop lip 50 extending around the inside 48 of the open end 26 of the exhaust gas pipe 28. The stop lip 50 comprises for example a flange formed at the open end 26 of the exhaust gas pipe 28. A heat-resistant seal 52 in the form of a braided glass or ceramic fibre cord may additionally be introduced into the flange.
According to
While the present invention has been described in conjunction with a specific embodiment, it is understood that many alternatives, modifications and variations will be apparent to those skilled in the art in light of the foregoing description. For example, although the vehicle 10 shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 102009046253.8 | Oct 2009 | DE | national |
