Patent Application
20140245723
The invention relates to a delivery device for delivering a liquid additive out of a tank to an exhaust-gas treatment device. Exhaust-gas treatment devices to which a liquid additive is supplied are widely used, in particular, in the automotive field. An exhaust-gas purification method particularly commonly implemented in such exhaust-gas treatment devices is the selective catalytic reduction (SCR) method in which nitrogen oxide compounds in the exhaust gas are converted with the aid of a reducing agent to form non-harmful substances (for example water, nitrogen and/or CO2). The reducing agent is often supplied to such exhaust-gas treatment devices in the form of a liquid additive, in particular in the form of a urea-water solution. A urea-water solution with a urea content of 32.5 percent is available for that purpose under the trademark AdBlue®. The invention also relates to a method for compensating the formation of ice in a delivery device and a motor vehicle having a delivery device.
In order to supply the liquid additive to the exhaust-gas treatment device, a delivery device is generally required which transports the liquid additive from the tank to the exhaust-gas treatment device. A delivery device should operate with the highest possible dosing accuracy, should be as inexpensive as possible and should have as long a service life as possible.
If reducing agent is used as the liquid additive, it is a technical problem that such aqueous reducing agents freeze at temperatures that may arise during normal operation of a motor vehicle.
The urea-water solution AdBlue® commonly used as reducing agent for exhaust-gas purification freezes, for example, at −11° C. In the case of motor vehicles, such low temperatures may arise, in particular, during long standstill periods in winter. As a liquid additive freezes, the additive generally increases in volume. That increase in volume can damage the delivery device. A delivery device should therefore, if appropriate, be constructed in such a way that it is not damaged by an increase in volume of the additive and by the associated ice pressure that is generated.
It is accordingly an object of the invention to provide a delivery device for delivering a liquid additive out of a tank, a method therefor and a motor vehicle having a delivery device, which overcome the hereinafore-mentioned disadvantages and solve, or at least lessen, the highlighted technical problems of the heretofore-known devices, methods and vehicles of this general type as advantageously as possible. It is sought, in particular, to describe a particularly advantageous delivery device for delivering a liquid additive. Furthermore, it is sought to specify a particularly advantageous method for compensating the formation of ice in a delivery device.
With the foregoing and other objects in view there is provided, in accordance with the invention, a delivery device for delivering a liquid additive out of a tank to an exhaust-gas treatment device, comprising at least a delivery duct with an overall volume and a pump disposed in the delivery duct, the delivery duct having, downstream of the pump in a delivery direction, a flexible wall portion which, with an outer side situated opposite the delivery duct, bears against a stop when the pressure in the delivery duct lies in a predefined operating pressure range. A spring element which is provided on the outer side is constructed to deform the flexible wall portion in such a way that the overall volume of the delivery duct is reduced in size when the pressure in the delivery duct is lower than a threshold pressure.
The delivery device preferably has a suction point at which the liquid additive can be suctioned out of a tank. A tank typically has an interior space, in which the liquid additive is stored, and a tank wall, which has a tank base and a tank top side and which delimits the interior space. The suction point either may be in direct contact with the interior space of the tank or is connected through a line piece to the interior space of the tank.
The delivery device furthermore preferably has an outlet port. The liquid additive is provided at the outlet port. The outlet port is preferably connected through a line to an injection device. The injection device may be disposed on an exhaust-gas treatment device and constructed to supply the liquid additive into the exhaust-gas treatment device. The injection device may include a nozzle for injecting the liquid additive into the exhaust-gas treatment device and/or a valve for controlling the amount of additive supplied into the exhaust-gas treatment device.
In the described delivery device, preferably reducing agent (or a reducing agent precursor which forms ammonia) and particularly preferably aqueous urea solution is used as liquid additive. The method of selective catalytic reduction is carried out using the reducing agent in an exhaust-gas treatment device.
The delivery device is preferably disposed directly on/in the tank for storing the liquid additive. The delivery device is preferably disposed in a separate chamber disposed on or at least partially in the tank. The exhaust-gas treatment device preferably includes, in addition to the injection device, an SCR catalytic converter in which the SCR method can be carried out with the aid of a reducing agent which is provided as the liquid additive to the exhaust-gas treatment device.
The delivery duct preferably forms a portion of a flow path for the liquid additive from the tank to the exhaust-gas treatment device. The overall volume of the delivery duct preferably refers to the volume which the delivery duct has in the delivery device and which is filled with the liquid additive during the operation of the delivery device. The overall volume refers, in particular, to the volume which the delivery duct has downstream of the pump in the delivery direction of the liquid additive and which is filled with liquid additive. The pump is connected to the delivery duct. The pump preferably forms a portion of the delivery duct. The pump divides the delivery duct into a suction portion from the suction point to the pump and a pressure portion from the pump to the outlet port. The overall volume may, in particular, be formed only by the pressure portion of the delivery duct. It is preferable for at least one valve to be provided in the pump, which valve predefines a delivery direction of the liquid additive through the pump. For this reason, the liquid additive cannot flow through the pump counter to the delivery direction. Furthermore, the pump has a movable pump element which can perform a delivery movement. Due to the delivery movement, the liquid additive is delivered through the pump.
The delivery duct has a duct wall. The duct wall is preferably formed for the most part in the manner of a bore in a plate. The flexible wall portion is preferably not fixedly connected to the plate, or not a fixed constituent part of the plate. Those wall portions of the delivery duct which are formed by the plate are, on the whole, rigid. The flexible wall portion is preferably composed of a flexible material. The flexible wall portion may be formed by a flexible diaphragm, for example. The flexible wall portion or the flexible diaphragm may be formed, for example, from plastic, in particular from rubber. The flexible wall portion is preferably reversibly/elastically deformable. The flexible wall portion or the flexible diaphragm is preferably formed by an areal element. The areal element has a first surface and a second surface. The first surface is directed toward the delivery duct and forms the flexible wall portion. The second surface forms the outer side which is situated opposite the delivery duct and the first surface. The stop against which the opposite outer side bears is formed, for example, by a cap element or a cover which makes contact with the outer side. The spring element is preferably disposed between such a cap and the outer side of the flexible wall portion.
The operating pressure range lies preferably at pressures above 3 bar. The operating pressure range lies particularly preferably between 5 bar and 10 bar and very particularly preferably between 7 bar and 9 bar. The spring element is constructed to push or press the flexible wall portion into the delivery duct or into the overall volume when the pressure in the delivery duct is lower than a threshold pressure. The threshold pressure lies preferably below the lower limit of the operating pressure range, and therefore preferably below 3 bar. The flexible wall portion may have a construction which promotes a deformation. For example, the flexible wall portion may have provided on it corrugations which promote a deformation of the flexible wall portion.
In accordance with another particularly advantageous feature of the delivery unit of the invention, a return line branches off from the delivery duct downstream of the pump in the delivery direction (in the region of the pressure portion of the delivery duct), which return line can be closed off by a return valve. The return line branches off from the pressure portion in order to be able, by using the return valve, to ensure a release of pressure from the pressure portion if appropriate. A return flow of liquid additive through the pump is prevented by the valve provided in the pump, as described further above. A release of pressure from the pressure portion of the delivery duct through the pump is therefore prevented. A release of pressure from the pressure portion through the outlet port would lead to a loss of liquid additive, because the additive discharged through the outlet port passes to the injection device. A loss-free release of pressure is possible, in particular, through the return line. When the flexible wall portion deforms, the liquid additive which is displaced out of the delivery duct due to the reduction in size of the overall volume can escape through the return line.
In accordance with a further particularly advantageous feature of the delivery unit of the invention, disposed on the stop is at least one force sensor which can measure the force exerted on the stop by the flexible wall portion. A pressure in the delivery duct can thus be determined. The flexible wall portion maintains its flexibility even when it is bearing against the stop. The flexible wall portion then transmits (at all points) the force exerted by the pressure in the delivery duct directly to that region of the stop which is situated (directly) opposite. Through the use of a force sensor integrated in the stop, the situation can be utilized in order to carry out a measurement of the pressure in the delivery device or in the delivery duct of the delivery device. The pressure sensor is preferably integrated into the stop so as to end flush with the stop. The force sensor may also protrude slightly beyond the stop in order to ensure that a force exerted on the flexible wall portion is transmitted more easily to the force sensor. During operation (when the flexible wall portion bears against the stop), the outer side of the flexible wall portion presses against the force sensor. The force actually acting on the force sensor is also defined by the surface area of the force sensor (or the surface area of the flexible wall portion pressing against the force sensor). The surface area of the force sensor is multiplied by the pressure in the delivery duct in order to calculate the force exerted. The surface area of the force sensor is preferably relatively small in relation to the overall surface area of the stop against which the flexible wall portion bears. The surface area of the sensor amounts to preferably at most 1/10, and particularly preferably at most 1/20, of the overall surface area of the stop. Conventionally used force sensors measure an exerted force on the basis of a change in length or a deformation of an elastic material with a known modulus of elasticity. Therefore, a slight deformation of the flexible wall portion takes place at the force sensor even in the presence of the operating pressure in the delivery duct because the flexible wall portion deforms, in the region of the sensor, toward the sensor so as to transmit a force from the outer side to the force sensor. The deformation is preferably as small as possible in order to ensure a small change in the overall volume of the delivery duct within the operating pressure range.
The force sensor is preferably formed by a piezo material and/or by a deformable (electrical) resistance. A piezo material generates a different voltage according to how intensely it is deformed. In the case of a deformable resistance, the electrical resistance changes as a function of a deformation. The deformation is in each case proportional, based on the modulus of elasticity, to the acting force. The generated electrical voltage is in each case proportional to the deformation. An acting force can thus be converted into electrical voltage and evaluated by electronics.
In accordance with an added particularly advantageous feature of the delivery unit of the invention, the pump has a pump outlet and the delivery duct has a chamber downstream of the pump outlet in the delivery direction, the pump outlet opens into the chamber, and the flexible wall portion is disposed on the chamber opposite the pump outlet.
The chamber is, in particular, an extension of the delivery duct. The chamber is preferably formed as a recess which is situated on a plate of the delivery device. A portion of the delivery duct which extends from the pump outlet opens into the chamber. A further portion of the delivery duct which extends to the outlet port branches off from the chamber. Since the chamber is provided as a recess in the plate, the chamber can be covered by an areal element which forms the flexible wall portion. This yields a particularly simple possibility for mounting the flexible wall portion of the delivery duct. A cap which forms the stop can then be inserted in the described recess in the plate, at the outer side of the flexible element or material which forms the flexible wall portion.
The pump outlet of the pump is preferably aligned along a common axis with a pump inlet of the pump. During delivery operation, the additive exits the pump outlet as a pulsating flow with pressure fluctuations. The described chamber is also advantageous from a flow aspect. The pulsating flow from the pump outlet is homogenized in the chamber. This arises, in particular, due to the enlarged volume of the chamber and/or the diversion of the flow which occurs when the additive exits the chamber again.
The chamber and the flexible wall portion are preferably disposed spatially on a common axis with the pump inlet and the pump outlet. An axis running through the pump inlet and the pump outlet preferably intersects the chamber and the flexible wall portion. The chamber is delimited by the flexible wall portion preferably on a side situated opposite the pump outlet or the pump.
In accordance with an additional particularly advantageous feature of the delivery unit of the invention, the stop has a receptacle in which the spring element is accommodated when the flexible wall portion bears against the stop.
Such a receptacle makes it possible for the spring element to behave rigidly when the pressure in the delivery duct lies in the operating pressure range. The spring element is then accommodated entirely in the receptacle and, in this case, is preferably compressed. If the stop is formed by a cap, the receptacle may be formed as a recess of the cap. For a spring element constructed as a spiral spring, the receptacle may be formed, for example, as an annular groove in the cap, the diameter of which groove corresponds to the diameter of the spring and the depth of which groove is sufficient to completely accommodate the spring element in the compressed state.
In accordance with yet another particularly advantageous feature of the delivery unit of the invention, the spring element exerts on the flexible wall portion a spring force which corresponds to a pressure of 0.2 to 1.0 bar in relation to the surface area of the flexible wall portion when the flexible wall portion bears against the stop. Through the use of a force corresponding to such a pressure, the liquid additive can be forced out of the overall volume of the delivery duct of the delivery device even if a certain counter-pressure is acting on the delivery device from the outside. The liquid additive should preferably be forced through a return line back into a tank. The delivery device is preferably disposed on the base of a tank. The pressure acting on the delivery duct or on the overall volume is defined substantially by the filling level in the tank if the delivery device is disposed on the tank base and a return valve in a return line which connects the delivery duct to the tank interior space is open. A pressure of 0.2 to 1.0 bar then corresponds to the threshold pressure above which the overall volume in the delivery duct is reduced in size. The threshold pressure is preferably selected in such a way that an adequate spacing from the operating pressure range is obtained and it is thus ensured, that the delivery device behaves substantially rigidly when the pressure lies in the operating pressure range and a reduction in size of the overall volume occurs only when an operational stoppage of the delivery device actually takes place and the return valve in a return line is open. The spring force of the spring element required to ensure the above-specified values for the threshold pressure may be determined and fixed on the basis of the desired threshold pressure and the surface area of the flexible wall portion on which the spring element acts and which is exposed to the pressure in the delivery duct.
The outer side of the flexible wall portion is preferably connected to the environment through an exchange duct in such a way that a pressure acting on the outer side of the flexible wall portion does not exert a force which distorts the behavior (in particular the pressure-deformation characteristic curve) of the flexible wall portion.
A force exerted by the spring element on the flexible wall portion is, if appropriate, also taken into consideration in the determination of the pressure in the delivery duct. A part of the pressure in the delivery duct may be compensated by the spring element in such a way that the force sensor can measure only a part of the pressure. In order to be able to measure the pressure in the duct, it is necessary, if appropriate, to take into consideration that pressure component of the pressure measured by the force sensor which is compensated by the spring element.
With the objects of the invention in view, there is furthermore provided a method for compensating the formation of ice in a delivery device having an overall volume of a delivery duct being at least partially filled with liquid additive, wherein the method comprises at least the following steps:
The method according to the invention may be implemented or carried out, in particular, with the delivery device according to the invention. The advantages and structural features explained with regard to the described delivery device can be transferred analogously to the described method. The same applies to the advantages and special configuration features of the method according to the invention described below, which can be transferred analogously to the delivery device according to the invention.
A compensation of the formation of ice refers in this case, in particular, to a compensation of the volume expansion which normally arises in conjunction with the formation of ice, or of the generated ice pressure of the additive. The volume expansion is obtained by an increase in size of the volume provided for the additive.
The stoppage of the operation of a pump in step a) is usually associated with the stoppage of an internal combustion engine connected to an exhaust-gas treatment device, to the exhaust-gas treatment device of which internal combustion engine the delivery device is connected in order to supply the liquid additive.
The opening of the return valve in a return line in step b) normally takes place automatically. The return valve is preferably constructed as a solenoid valve which is closed when an electrical current is applied and which is open when no electrical current is applied. Upon the stoppage of operation, an electrical current supply to the delivery device is preferably interrupted. The return valve in the return line then opens automatically and produces a connection between the overall volume of the delivery duct and a tank through the return line. As a result of this, the pressure in the overall volume falls because the pressurized liquid additive in the delivery duct or in the overall volume can escape through the return line.
In step c), the overall volume can then be reduced in size with relatively little force. In this case, an active reduction in size means that a component of the delivery unit is provided for initiating or carrying out a process of reducing the size of the overall volume. This may be realized, for example, by a spring which deforms a flexible wall portion of the delivery duct into the delivery duct. It is, however, also possible, in a further embodiment of the method, for a mechanically actuable device (if appropriate with an electric drive) to actively reduce the size of the overall volume. For example, a slide element may be moved into the overall volume in order to reduce the size of the overall volume.
As a result of the deformation, the liquid additive is, in step d), forced through the return valve and through the return line into the tank. There is a temporary flow of the liquid additive out of the overall volume through the return line and back into the tank.
As long as the temperature (to which the delivery device is exposed) does not fall far enough to cause liquid additive to solidify into ice, the overall volume of the delivery duct does not change. If the temperature falls further and the formation of ice in the delivery duct of the delivery device begins, the overall volume increases in size again in step e) to the extent required for compensating the freezing. In this case, a passive increase in size means, in particular, that the increase in size is not realized by an actively moved component of the delivery unit but rather is dependent on external circumstances (in the present case, the volume expansion of water-based additives when freezing occurs). The compensation of the freezing or of the volume expansion which takes place when freezing occurs preferably takes place again (only) by a deformation of the flexible wall portion. The deformation which occurs in step e) preferably opposes the active deformation provided in step c).
For clarity, it is pointed out in this case again that (if this does not emerge from the above description itself) steps a)-d) take place in the specified sequence when freezing occurs.
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 purification of exhaust gases of the internal combustion engine, a tank for a liquid additive, and a delivery device described according to the invention which is constructed to deliver the liquid additive from the tank to the exhaust-gas treatment device.
The delivery device of the motor vehicle is particularly advantageously also suitable for carrying out the described method.
Other features which are considered as characteristic for the invention are set forth in the appended claims, noting that the 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 structural variants of the invention being specified.
Although the invention is illustrated and described herein as embodied in a delivery device for delivering a liquid additive out of a tank, a method therefor and a motor vehicle having a delivery 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 in which size ratios are diagrammatic, and first, particularly, to
The concept of providing delivery ducts in a delivery device with an angle of inclination may also be implemented independently of the concept, described further above, of a delivery device having a flexible wall portion. In particular, there is also specified herein a delivery device having at least one delivery duct and having a pump for delivering reducing agent from a suction point in a tank to an outlet port, in which all of the ducts in the delivery device are at an angle of at least 2°, in such a way that from any point of the delivery duct, a flow path for an air bubble to a return valve exists which (in terms of the geodetic position of the air bubble) rises monotonously. Such a delivery device may be supplemented as desired with further features from the description. It is thereby possible, specifically for the field of application mentioned in the introduction, for the formation of gas bubbles in the ducts to be reduced, or for the migration of the gas bubbles in the delivery unit to be influenced in a targeted manner. It is thereby possible to obtain a reduction not only in pressure fluctuations but also, for example, in malfunctions in the delivery of the heating of frozen reducing agent and/or servicing and monitoring measures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102011118628.3 | Nov 2011 | DE | national |
This is a continuation, under 35 U.S.C. §120, of copending International Application No. PCT/EP2012/071530, filed Oct. 31, 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 118 628.3, filed Nov. 16, 2011; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2012/071530 | Oct 2012 | US |
| Child | 14279581 | US |
