Patent Application
20140174058
The invention relates to a device for providing liquid reducing agent for an exhaust-gas treatment device and a motor vehicle having the device.
In the automotive field in particular, widespread use is made of exhaust-gas treatment devices into which an additional substance is fed for the purification of the exhaust gas of an internal combustion engine. An exhaust-gas purification method particularly widely used in such exhaust-gas treatment devices is the process of selective catalytic reduction (the SCR process). In that method, a reducing agent is supplied to the exhaust gas. Nitrogen oxide compounds in the exhaust gas can be reduced by the reducing agent. Ammonia is generally used as reducing agent. Ammonia is normally not stored in motor vehicles directly but rather in the form of a precursor solution which can be converted to form ammonia. The conversion may be performed within the exhaust-gas treatment device and/or in an additional reactor provided for that purpose. The reactor may be disposed in the exhaust line and/or outside the exhaust line. An aqueous urea solution may be used, for example, as a reducing agent precursor. A 32.5% urea-water solution is available as a reducing agent precursor under the trademark AdBlue®. The expressions “reducing agent” and “reducing agent precursor solution” and “reducing agent precursor” will hereinafter be used synonymously for one another.
In order to provide the reducing agent for an exhaust-gas treatment device in a motor vehicle, a tank is normally provided for the reducing agent and a delivery unit is provided for delivering the reducing agent from the tank to the exhaust-gas treatment device. The tank and the delivery unit should be as inexpensive as possible, and should at the same time ensure reliable provision of the reducing agent. It has proven to be a problem, in particular, that the reducing agent in the tank contains impurities that can cause damage to the delivery unit or to an injector for the injection of the reducing agent into the exhaust-gas treatment device. A delivery unit therefore typically has a filter by which impurities in the reducing agent can be retained.
It is accordingly an object of the invention to provide a device for providing liquid reducing agent and a motor vehicle having the device, which overcome the hereinafore-mentioned disadvantages and solve or at least alleviate the highlighted technical problems of the heretofore-known devices and vehicles of this general type. It is sought, in particular, to provide a particularly inexpensive device for the reliable provision of liquid reducing agent for an exhaust-gas treatment device.
With the foregoing and other objects in view there is provided, in accordance with the invention, a device for providing liquid reducing agent for an exhaust-gas treatment device, comprising a tank and a delivery unit with an intake or suction point in the tank at which reducing agent can be drawn-in from the tank. The intake point is covered by a partition layer in such a way that a closed intermediate space is provided between the intake point and the partition layer. The partition layer has a higher flow resistance for reducing agent in an outflow direction from the intermediate space into the tank than in an inflow direction from the tank into the intermediate space.
The intake point in the tank is preferably an opening in the wall of the tank. The opening is adjoined by a line which leads to the delivery unit. It is likewise possible for the intake point to be formed correspondingly on a delivery unit housing, which projects into the tank. The partition layer preferably forms a type of cover over the intake point. The partition layer may be constructed, for example, in the manner of a dome that is placed over the intake point. It is also possible for the intake point to be situated in a recess of the tank or in a recess of the tank wall, and for the partition layer to close off or cover that recess. In other words, the partition layer preferably spans the intake point.
The intermediate space is preferably situated between the partition layer and a tank wall in the region of the intake point. The flow resistance for reducing agent in the inflow direction or in the outflow direction is defined by the flow rate of reducing agent that can pass through the partition layer in the presence of a predefined pressure difference. The flow resistance need not be constant in the case of different pressure differences between the intermediate space and the tank. It is also possible for flow resistance to vary as a function of the pressure difference. Within the context of the invention, it is preferable for the flow resistance in the outflow direction to be significantly increased in relation to the flow resistance in the inflow direction, in particular, in the range of low pressures (pressures up to 0.2 bar and, in particular, pressures up to 0.1 bar). A pressure of 0.2 bar corresponds to a water column of 2 m [meters], and a pressure of 0.1 bar corresponds to a water column of 1 m [meter]. Pressures higher than that do not normally arise between the tank and the intermediate space. The pressure difference between the intermediate space and the tank is determined substantially by the mass flow of reducing agent through the partition layer and by the liquid levels in the intermediate space and in the tank, and also by the impact of the liquid in the case of sloshing movements in the tank and in the intermediate space. In the case of those effects, it is the case, in particular, that the fraction of the pressure difference arising from the occurring mass flow of reducing agent is negligible. Accordingly, the occurring pressure differences are determined substantially by the structural size of the tank, and very rarely exceed the value of 0.2 bar mentioned further above. Therefore, for the function of the partition layer, the way in which that partition layer behaves in the presence of relatively high pressure differences is less relevant. For example, it is possible for the flow resistances of the partition layer in the inflow direction and in the outflow direction to converge on one another again, or to fully equalize, in the presence of pressure differences of greater than 0.2.
Through the use of such a differing configuration of the flow resistances in the inflow direction and outflow direction, it can be ensured in regular operation that reducing agent that has passed through the partition layer into the intermediate space does not flow back, or flows back again only to a limited extent, into the tank.
A partition layer serves, in particular, to realize a spatial division of the intermediate space from the rest of the tank volume, which serves for example as an intermediate accumulator or reservoir for the delivery unit. The reducing agent situated therein may exhibit different properties (for example different cleanliness or different purity) than the reducing agent in the remainder of the tank.
The partition layer may also be equipped with a heater by which the reducing agent in the vicinity, in particular in the intermediate space, can be heated. The heater may, for example, include at least one heating element (in particular PTC heating elements) which is incorporated into the partition layer. For example, heating wires may be woven into the partition layer. The heater may also be constructed to heat the reducing agent in the tank, but the heater should serve primarily to heat the reducing agent in the intermediate space. The heat output by the heater is preferably initially output primarily into the intermediate space. When the reducing agent in the intermediate space is in liquid form, the heat from the heater also passes into the tank. For this purpose, the heater is preferably provided on an inner side, facing toward the intermediate space, of the partition layer.
The partition layer may preferably perform multiple or different functions during the provision of reducing agent, such as filtering, screening, heating or the like.
The partition layer may also have a fill level sensor for measuring the fill level in the tank. The fill level sensor may, for example, be in the form of electrical contacts that are fastened to the partition layer. It is likewise possible for the temperature to be inferred by checking the electrical resistance of a component (in particular of a heating element) of the partition layer.
In accordance with another advantageous feature of the device of the invention, the partition layer is only unidirectionally permeable to reducing agent in the inflow direction at least up to a threshold pressure difference of 0.01 bar to 0.1 bar between the tank and the intermediate space.
Through the use of such a configuration of the partition layer, it is possible, at least in the range of pressure differences that arise between the tank and intermediate space during regular operation, to completely prevent reducing agent from flowing from the intermediate space back into the tank. The action of the partition layer is thus particularly effective.
A partition layer of this type may be a semi-permeable structure, that is to say in other words, in particular, a structure which is semi-permeable, that is to say which allows only certain substances (reducing agent fractions) to pass through and/or allows substances to pass through in only one (single) direction. The diaphragm may, for example, include multiple layers of a textile fabric, wherein in particular, a Teflon® layer (polytetrafluoroethylene) is provided.
A partition layer of this type may be composed of a combination of a filter ply/screen ply with a sponge on the filtered side (in the present case on the inner side). The sponge may be in the form of a thin sponge ply that bears against the filter ply/screen ply and/or is fixedly connected to the filter ply/screen ply. The sponge ply is preferably thinner than 2 mm [millimeters] and is particularly preferably thinner than 1 mm. Capillary forces act in the sponge or in the sponge ply. The partition layer retains a volume of reducing agent due to the capillary forces. A barrier ply is thus formed which prevents a backflow of the reducing agent through the filter ply/screen ply.
In accordance with a further advantageous feature of the device of the invention, the partition layer is a filter which has at least one barrier ply that increases the flow resistance of the partition layer in the outflow direction.
The barrier ply imparts a barrier action in the outflow direction at least in the range of low pressure differences between the intermediate space and the tank. This means that the barrier ply prevents a flow of reducing agent out of the tank.
A barrier ply of this type may also be formed with a suitable semi-permeable structure. A barrier ply may, if appropriate, also have a multi-layer form in order to ensure an improved barrier action.
The partition layer may thus have a filtering action. Reducing agent flowing into the intermediate space is filtered. It is thus possible for impurities in the reducing agent in the tank to be kept away from the intake point. Impurities are prevented from passing into the intermediate space and to the intake point. At the same time, as a result of the increased flow resistance in the outflow direction, it is ensured that reducing agent that has already been filtered does not pass out of the intermediate space back into the tank. It is thus possible to prevent reducing agent from being filtered twice. At the same time, a reservoir of filtered reducing agent is situated in each case in the intermediate space in the direct vicinity of the intake point.
The barrier action and the filtering action may be realized in two different plies of the partition layer. Then, in addition to the barrier ply, there is preferably also provided a filter ply that performs the filtering action. The partition layer is then of multi-layer form. The barrier ply and the filter ply may also be realized in a common ply which combines the described barrier action and the described filtering action with one another. The combined filter ply and barrier ply may, for example, have pores and/or ducts which (under normal operating conditions) are permeable to reducing agent, and retain particles that are larger than the pores or ducts, in the inflow direction, and which are permeable neither to reducing agent nor to such particles in the outflow direction.
In accordance with an added feature of the device of the invention, the partition layer is a screen which has at least one flow-impeding device that increases the flow resistance of the partition layer in the outflow direction.
Through the use of a screen, it is likewise possible for reducing agent to be purified as it passes out of the tank into the intermediate space. A screen has openings of a uniform size. The openings may, for example, have a uniform diameter of less than 1 mm [millimeter], preferably of less than 0.5 mm [millimeters] and particularly preferably of between 10 μm [micrometers] and 20 μm. Through the use of a screen, particles in the reducing agent can be retained in such a way that they do not pass into the intermediate space and thus also do not pass to the intake point. In order to increase the flow resistance from the intermediate space back into the tank, it is possible, in the case of the embodiment of the partition layer as a screen, for at least one flow-impeding device to be provided. Flow-impeding devices may, for example, be valve devices which close the openings of the screen upon the onset of a backflow from the intermediate space into the tank (in the outflow direction). Flow-impeding devices or valve devices may, for example, be movable vanes which are fastened to the screen on one side and which cover the openings of the screen in the case of a flow proceeding from that side of the screen which has the vanes. In the case of the partition layer in the form of a screen in the described device, the vanes are preferably fastened to that side of the screen which faces the intermediate space. A backflow from the intermediate space into the tank (in the outflow direction) can be prevented in an effective manner by the vanes.
In accordance with an additional advantageous feature of the device of the invention, the delivery unit is disposed in a chamber which is disposed at least partially in the tank, and the partition layer surrounds the chamber in such a way that an encircling intermediate space is provided between the chamber and the partition layer.
The partition layer surrounds the chamber preferably in a radially encircling manner in such a way that, for example, an encircling, in particular annular intermediate space is provided between the chamber and the partition layer. The chamber is preferably a constituent part of the tank bottom. The chamber preferably extends upward into the tank volume from the tank bottom. The chamber, however, extends preferably at most over 30%, and particularly preferably at most over 15%, of the tank height. In the case of this type of construction, the intake point may be situated on the chamber and thus in the direct vicinity of the delivery unit and simultaneously in the vicinity of the tank bottom, in such a way that the reducing agent can be drawn in from the tank through the intake point as completely as possible.
A spacer structure may also be provided between the chamber and the partition layer for ensuring spacing between the chamber and the partition layer. It is thus possible for an adequately large reservoir for filtered reducing agent to be provided between the chamber and the partition layer. Due to the properties of the partition layer, the reducing agent does not flow out of the reservoir back into the tank, or flows out of the reservoir back into the tank only in a time-delayed manner. It can thus be achieved that reducing agent is available at the intake point in each case during cornering and in the event of sloshing movements in the tank.
In accordance with yet another advantageous feature of the device of the invention, at least one guide structure is disposed in the tank around the partition layer, which guide structure guides the reducing agent toward the partition layer.
The guide structure may, for example, be in the form of guide plates that guide the reducing agent toward the partition layer if the tank is in an oblique position or in the event of sloshing movements in the tank. It can thus be achieved that the reducing agent in the tank collects in front of the outside of the partition layer and is conducted into the intermediate space. Due to the increased flow resistance in the outflow direction, the reducing agent does not flow out of the intermediate space again, or flows out of the intermediate space again only at a significantly slower rate. Thus, even if the tank is in an oblique position or in the event of sloshing movements in the tank, an amount of reducing agent remains in each case in the intermediate space in the direct vicinity of the intake point, in such a way that the delivery of reducing agent by using the delivery unit is not interrupted. This is the case even if the reducing agent fill level in the tank is already greatly depleted.
In accordance with yet a further advantageous feature of the device of the invention, the partition layer is permeable to air bubbles in the outflow direction from the intermediate space. It is thus possible for air bubbles to be prevented from collecting in the intermediate space. Suitable semi-permeable materials that are permeable to reducing agent only in one direction and which thus act as a barrier ply may be permeable to air bidirectionally, that is to say in both directions. With diaphragms composed of materials of this type, it is possible to realize permeability of the partition layer to air bubbles.
In accordance with yet an added advantageous feature of the device of the invention, the partition layer promotes a flow of heat in the inflow direction and reduces the flow of heat in the outflow direction.
It is thus possible to prevent a situation in which, when freezing occurs, the reducing agent in the intermediate space freezes more quickly than that in the tank. It is preferable for liquid reducing agent to remain in the intermediate space when the reducing agent in the tank has already frozen. It is thus possible to realize a situation in which, upon start-up of the delivery unit, liquid reducing agent may be directly present at the intake point even though the reducing agent in the tank is largely frozen. It is therefore not necessary for the intermediate space to be initially melted free by using a heater.
In accordance with yet an additional advantageous feature of the device of the invention, the partition layer has a support structure which imparts stability to the partition layer, wherein the flow resistance of the support structure for reducing agent is negligible in the inflow direction and in the outflow direction.
The flow resistance is, in particular, negligible in relation to the flow resistance of further plies of the partition layer. The support structure thus exhibits practically no relevant filtering action and rather serves merely to predefine the shape and position of the partition layer. The support structure may, for example, be implemented as a sheet-metal construction which surrounds the further plies of the partition layer and/or to which the further plies of the partition layer are applied. The support structure may, for example, form at least one frame for the partition layer. The support structure may be in the form of a framework construction which spans a beam-type skeleton to which the further plies of the partition layer can be applied. A support structure is advantageous, in particular, if the partition layer includes a filter, because a filter normally exhibits relatively low mechanical stability and the filter can thus be held in position, and/or in the intended shape, in particularly advantageous fashion by using a support structure. The support structure and further plies (for example a filter ply, a heat protection ply and/or a barrier ply) of the partition layer may also be connected to one another. It is, for example, possible for the support structure to partially extend through further plies of the partition layer and/or to penetrate partially into further plies of the partition layer and for the support structure to thereby mechanically hold further plies of the partition layer. Further plies of the partition layer may also be welded or adhesively bonded to the support structure. The connection between the partition layer and the support structure may also be formed in linear regions (for example at the edges of the partition layer) and/or areally.
In a further advantageous embodiment of the device, the properties of the partition layer vary over the area of the partition layer. This means, in particular, that the partition layer has varying properties at least in sections. It is preferable for the area of the partition layer to be divided into at least two zones, wherein the properties of the partition layer are different in the zones. It is also possible for the properties of the partition layer to vary in continuous fashion as viewed over the area of the partition layer.
In this case, “properties of the partition layer” refers to the properties already described further above, such as for example the unidirectional permeability or the bidirectional permeability of the partition layer to reducing agent and/or to air, or the flow resistance of the partition layer for reducing agent and/or for air in the inflow direction and in the outflow direction.
It is particularly preferable for the partition layer to have a first zone and a second zone, wherein (in the intended installation orientation of the device) the first zone is situated above the second zone, wherein the partition layer, in the second zone, has a higher flow resistance for reducing agent in an outflow direction from the intermediate space into the tank than in an inflow direction from the tank into the intermediate space, and wherein the partition layer, in the first zone, has an improved permeability in relation to the second zone. It is preferable, in particular, for the first zone to exhibit improved permeability to air in the outflow direction.
Furthermore, it is preferable for the partition layer to be constructed at least partially from a first material in the first zone and to be constructed at least partially from a second material in the second zone, wherein the first material and the second material exhibit different properties, in particular, with regard to permeability to air and/or to reducing agent. It is preferable for the second material for the partition layer to not be used in the first zone and for the first material for the partition layer to not be used in the second zone. The first material preferably exhibits improved permeability to air in relation to the second material. The second material preferably exhibits different flow resistances for reducing agent in the two through flow directions (in an inflow direction and in an outflow direction). The second zone of the partition layer preferably forms a space in which reducing agent collects during operation of the device. Air bubbles in the intermediate space between the intake point and the partition layer can thus escape from the intermediate space through the first zone.
With the objects of the invention in view, there is concomitantly provided a motor vehicle, comprising an internal combustion engine, an exhaust-gas treatment device for the purification of the exhaust gases of the internal combustion engine, and a device which is constructed to supply reducing agent to the exhaust-gas treatment device. The exhaust gas from the internal combustion engine flows through the exhaust-gas treatment device in an exhaust-gas flow direction. The device conducts the reducing agent to the exhaust-gas treatment device through an injector. The injector is constructed to inject the reducing agent into the exhaust-gas treatment device. The injector may either be a self-opening nozzle or may, by using an actuable valve element, control the flow rate of reducing agent supplied to the exhaust-gas treatment device. In the exhaust-gas treatment device there is disposed an SCR catalytic converter in which the SCR process for exhaust-gas purification is performed. In this case, nitrogen oxide compounds in the exhaust gas are converted with the aid of the reducing agent to form non-hazardous substances such as water, carbon dioxide and nitrogen.
It may also be advantageous for at least one fill level sensor to be disposed and/or integrated in and/or on the partition layer. The fill level of the reducing agent in the tank can be monitored by using a fill level sensor. The fill level sensor may be a continuous fill level sensor which permits permanent monitoring of the fill level in a range between a minimum measurable fill level and a maximum measurable fill level. The fill level sensor may also exhibit discrete characteristics. A discrete fill level sensor can detect only whether reducing agent is present at (at least) a certain level in the tank, and the fill level in the tank is thus above the level monitored by the fill level sensor. In particular, in the case of discrete fill level sensors, it is expedient for multiple fill level sensors to be disposed in and/or on the particle screen. It is thus possible to obtain more precise information regarding the fill level in the tank.
The at least one fill level sensor may, for example, be realized in the form of an electrical conductor and/or in the form of an electrical contact. The measurement of the fill level may preferably be performed by using an electrical resistance and/or electrical capacitance. The electrical resistance and/or electrical capacitance between two electrical contacts or two electrical conductors changes as a function of whether or not reducing agent is present at/between the contacts or at/between the conductors. This can be utilized for the determination of the fill level. The electrical contacts and/or the electrical conductors may, for example, be adhesively bonded, welded and/or soldered or brazed to the partition layer. At least one ply (support ply, barrier ply, etc.) of the partition layer may also be implemented as a fabric or mesh. The electrical contacts and/or electrical conductors may then be woven or braided into the ply.
Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that features specified individually in the claims may be combined with one another in any desired technologically meaningful way and may be supplemented by explanatory facts from the description, with further embodiments of the invention being highlighted.
Although the invention is illustrated and described herein as embodied in a device for providing liquid reducing agent and a motor vehicle having the device, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.
Referring now in detail to the figures of the drawing for explaining the invention and the technical field in more detail by showing particularly preferred structural variants to which the invention is not restricted, and first, particularly, to
It is possible in each case to see the device 1, having a tank 3 in which a reducing agent can be stored as well as a delivery unit 4 disposed in a chamber 9. The chamber 9 is a constituent part of a tank bottom 25 or is inserted into the tank bottom 25. An intake point 5 through which reducing agent can be drawn-in, is situated on the chamber 9 in the region of the tank bottom 25. The delivery unit 4 has a pump 17 for drawing-in reducing agent. The delivery unit 4 and the chamber 9 are surrounded by a partition layer 6. At the same time, the partition layer 6 covers the intake point 5, so that an intermediate space 7 is formed between the partition layer 6 and the intake point 5 or between the partition layer 6 and the delivery unit 4 or between the partition layer 6 and the chamber 9. There is an inflow direction 23 from the tank 3 through the partition layer 6 into the intermediate space 7. Furthermore, there is an outflow direction 24 from the intermediate space 7 through the partition layer 6 back into the tank 3. Reducing agent drawn-in at the intake point 5 is made available by the delivery unit 4 at a line connector 16 to which there can be connected a line through which the reducing agent can be conducted to an exhaust-gas treatment device.
In
In the embodiment according to
An exemplary configuration of the screen 19 of
It is clear that a person skilled in the art may readily combine the content of the disclosure of the figures and associated explanations, in such a way that details of one embodiment may be used together with details of another embodiment. The only exceptions to this are where explicitly stated above.
A particularly inexpensive device for the reliable provision of liquid reducing agent for an exhaust-gas treatment device has thus been proposed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102011112325.7 | Sep 2011 | DE | national |
This is a continuation, under 35 U.S.C. §120, of copending International Application No. PCT/EP2012/066363, filed Aug. 22, 2012, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2011 112 325.7, filed Sep. 2, 2011; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2012/066363 | Aug 2012 | US |
| Child | 14195093 | US |
