Patent Application
20140338311
1. Field of the Invention
The invention relates to a method for operating a dosing or metering apparatus for providing a liquid additive. The dosing apparatus may, for example, be utilized for feeding a liquid additive into an exhaust-gas treatment apparatus, where the liquid additive is used for the purification of the exhaust gases of a mobile internal combustion engine (in particular in a motor vehicle). The invention also relates to a motor vehicle having a dosing or metering apparatus.
Exhaust-gas treatment apparatuses into which a liquid additive is fed have become increasingly widely used in recent times. An exhaust-gas purification method particularly commonly implemented in such exhaust-gas treatment apparatuses is the selective catalytic reduction (SCR) method in which nitrogen oxide compounds in the exhaust gas are reduced with the aid of a reducing agent. The reducing agent is generally fed to the exhaust-gas treatment apparatus in the form of a liquid additive. A liquid additive particularly commonly used in this context is urea-water solution. A urea-water solution with a urea content of 32.5% is available under the trademaek AdBlue® and is widely used. The urea-water solution is merely a reducing agent precursor and is converted into ammonia (the reducing agent) outside the exhaust gas (in a reactor provided for that purpose) or in the exhaust gas (in the exhaust-gas treatment apparatus, under the action of the exhaust gas). Nitrogen oxide compounds in the exhaust gas are then, together with the ammonia, reduced in the presence of an SCR catalytic converter to form non-hazardous substances (water, CO2 and nitrogen). The invention is used in this technical field in particular.
The dosing apparatus for providing a liquid additive (urea-water solution) should be of the simplest possible construction and should be as durable, maintenance-free and inexpensive as possible. At the same time, it is desirable for the dosing accuracy of a dosing apparatus to be particularly high. In this way, it is possible firstly for the amount of liquid additive required for the conversion of pollutant constituents in the exhaust gas to be set in a particularly exact manner. It is furthermore possible for overdosing to be prevented in an effective manner.
It is accordingly an object of the invention to provide a method for operating a dosing apparatus and a motor vehicle having a dosing apparatus, which overcome the hereinafore-mentioned disadvantages and solve or at least alleviate the highlighted technical problems of the heretofore-known methods and vehicles of this general type. It is sought, in particular, to propose an especially advantageous method for operating a dosing apparatus for urea-water solution.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for operating a dosing apparatus for providing a liquid additive, in particular urea-water solution, the method comprising at least the following steps:
providing the dosing apparatus with at least the following:
The dosing apparatus particularly preferably serves for the dosing of a reducing agent (or of a reducing agent precursor such as urea-water solution) as a liquid additive into an exhaust-gas treatment apparatus of an internal combustion engine. The pump is preferably a diaphragm pump or a piston pump. The delivery rate of the pump is preferably not regulated. This means that an electronic regulator or controller, through the use of which the flow rate of additive delivered by the pump can be exactly set, is not provided. The tank is preferably connected to the pump through a suction line through which the pump can draw liquid additive out of the tank. The pressure accumulator is preferably disposed downstream of the pump as viewed in a flow direction of the liquid additive from the tank to the dosing valve. A pressure built up by the pump then prevails in the pressure accumulator. The pressure accumulator may, for example, be in the form of a flexible line that expands when liquid additive is delivered into the flexible line under pressure by the pump. The dosing valve is preferably an electrically controlled solenoid valve that can be opened and closed by the electric drive, wherein the opening time of the dosing valve predefines the amount of liquid additive provided. The pressure accumulator is also adjoined by a return valve. The return valve is preferably connected back to the tank through a return line in order to ensure that liquid additive present in the pressure accumulator can be discharged back into the tank.
The identification of a dosing demand in step a) preferably involves the identification of an electronic signal from an engine controller, which electronic signal is representative of a dosing demand. For example, an engine controller transmits a signal that corresponds to a certain flow rate of liquid additive required. The signal is detected, or identified, as a dosing demand. During step a), it is preferably the case that a pressure prevailing in the pressure accumulator is so low that handling of the dosing demand is not possible. It is preferably the case that, during step a), the pressure in the pressure accumulator is lower than 2 bar, particularly preferably lower than 1 bar and very particularly preferably lower than 0.5 bar. In step b), the pump is activated in order to build up a pressure in the pressure accumulator that is required in order to ensure that suitable dosing can be performed by using the dosing valve. In order to build up the pressure, a diaphragm pump or a piston pump is preferably operated with between 2 and 10 pump strokes. The number of pump strokes required to build up the required pressure in the pressure accumulator is dependent on the flexibility of the pressure accumulator and on the pressure difference between the pressure during step a) and the dosing pressure (step b). The more flexible the pressure accumulator, the more liquid additive can be delivered into the pressure accumulator in order for the required pressure to be built up. The greater the pressure difference, the more liquid additive can be delivered into the pressure accumulator. The pressure built up as a result of the activation of the pump in step b) is preferably between 3 and 10 bar, particular preferably between 5 and 10 bar and very particularly preferably between 6 and 8 bar. The pressure built up by the pump in step b) is typically slightly higher than the dosing pressure required in order to be able to perform precise dosing by using the dosing valve. The reason for this is that the pump is preferably unregulated. This means that the pump is not deactivated when a certain pressure is attained, and instead, the pump, after being activated, initially continues running regardless of the magnitude of the pressure prevailing in the pressure accumulator, which pressure acts counter to the pump.
In one structural variant of the described method, the operation of the pump ends only when the pressure in the pressure accumulator is so high that the pump can generate no further pressure increase in the pressure accumulator.
In accordance with another particularly preferable mode of the method of the invention, method steps a) to d) are performed repeatedly during the operation of the dosing apparatus.
In accordance with a further preferable mode of the method of the invention, in order to set the pressure in step c), the pressure is reduced, in particular by virtue of the return valve being opened. It is thus preferably provided that, in order to set a precise pressure in the pressure accumulator that is desired for being able to perform very precise dosing by using the dosing valve, the return valve is opened.
In accordance with an added preferable mode of the method of the invention, step b) continues to take place during step c). The return valve remains open and the pump is activated. Due to a return flow of liquid additive through the return valve, the pressure in the pressure accumulator remains constant.
In accordance with an additional preferable mode of the method of the invention, at least steps c) and d) are performed at least partially in parallel with one another. It is particularly preferable even for steps b), c) and d) to take place at least partially in parallel (at the same time).
The dosing valve is opened for the dispensing of the liquid additive through the dosing valve in step d). Liquid additive then flows out of the pressure accumulator through the dosing valve to a consumer for the liquid additive. The consumer for the liquid additive is preferably an exhaust-gas treatment apparatus in which the method of selective catalytic reduction is performed using the liquid additive. It is preferably the case that method steps b) and c) continue to take place during the execution of step d). During step d), the pump remains activated and continues to deliver liquid additive into the pressure accumulator. It is preferably also the case that, during step d), the return valve remains open and ensures that the pressure in the pressure accumulator is set to the dosing pressure, required for the dosing action, of for example a value between 5 and 10 bar, for example 7 bar. In this case, the return valve is preferably not open at all times, and is instead opened in pressure-controlled fashion every time the pressure in the pressure accumulator exceeds the dosing pressure. In this way, the pressure in the pressure accumulator is in each case repeatedly regulated to the dosing pressure during the dispensing of the additive through the dosing valve.
It is not necessary for the dosing valve to be open continuously for dispensing the additive in step d). It is also possible for the dosing demand identified in step a) to be dispensed in several pulses. In this case, a pulse corresponds in each case to one opening process and one closing process of the dosing valve.
If the method is executed repeatedly during the operation of the dosing apparatus, it is preferably the case that the pump is deactivated after method step d) in each case. The pump is then reactivated only when a new dosing demand is identified in a new step a). In particular, the pump does not run continuously during the operation of a delivery line and of a motor vehicle in which the dosing apparatus is disposed, and instead, the pump is generally activated only when a dosing demand is present.
In accordance with yet another advantageous mode of the method of the invention, a step e) of lowering the pressure in the pressure accumulator is performed after method step d). Method step e) is preferably also performed repeatedly together with method steps a) to d).
As a result of the lowering of the pressure in the pressure accumulator in step e), it is made possible for the pressure accumulator to be relieved of load between two dosing demands. The durability of the dosing apparatus can be increased in this way. In one structural variant, the pressure accumulator may be actively relieved of load. A return valve that branches off from the pressure accumulator may, if appropriate, be actively opened in step e) in order to permit an escape of the liquid additive from the pressure accumulator and thus ensure a lowering of the pressure in the pressure accumulator. The return valve may be identical to the return valve used in step c) of the method, and may be additionally capable of being actively opened in step e). It may, however, also be provided that, for step e), an additional return valve is provided which can be actively opened and which is disposed preferably in a parallel second return line from the pressure accumulator to the tank.
In a further structural variant of the method, it is also possible for active relief of load to be effected by using the pump of the delivery unit. In step e), the pump may, if appropriate, be operated counter to the delivery direction in order to deliver liquid additive out of the pressure accumulator and back into the tank in order that the pressure in the pressure accumulator decreases and the pressure accumulator is thus relieved of load.
It is also possible for the pressure accumulator to be passively relieved of load. For this purpose, it is possible for a leakage flow of liquid additive to flow back into the tank through a return valve and/or through the pump in step e), this resulting in a lowering of the pressure in the pressure accumulator. In the case of a passive relief of load in step e), the pressure in the pressure accumulator falls relatively slowly because the leakage flow is generally relatively small. The effect of the leakage flow on the pressure in the pressure accumulator during the dosing in step d) would otherwise be too great.
In accordance with yet a further advantageous mode of the method of the invention, the return valve is a passively opening valve, the opening pressure of which corresponds to the dosing pressure.
The return valve is preferably a passively opening valve which opens at a predetermined or preset threshold pressure, wherein the threshold pressure corresponds to the dosing pressure (the pressure with which the additive is dosed). The return valve preferably has a valve body and a valve spring which exerts a preload on the valve body. The return valve opens when the force exerted on the return valve by the liquid additive present in the pressure accumulator exceeds the spring force of the spring in the return valve. The use of a return valve of that type makes it possible to realize a particularly inexpensive dosing apparatus because no (electric) drive is required for the dosing valve, and also, no control unit is required for the control of the return valve.
The dosing apparatus can be implemented without an electrically driven dosing valve and/or without an (active) control unit of the return valve.
In accordance with yet an added advantageous mode of the method of the invention, the return valve is an actively opening valve with a valve drive, wherein a pressure sensor is disposed on the pressure accumulator and the return valve is controlled, with the aid of the valve drive, by a control unit in order to set the pressure in the pressure accumulator to the desired dosing pressure in step c).
The valve drive may, for example, be an electromagnet which exerts a force on an armature in the return valve, through the use of which force the return valve can be opened and/or closed. The pressure sensor may, for example, be in the form of an electronic pressure sensor which measures a pressure in the pressure accumulator and transmits it as an electrical signal to the control unit. The pressure information is then processed in the control unit in order to specify whether the check or return valve is to be opened and/or closed (regulating loop).
In accordance with yet an additional advantageous mode of the method of the invention, the pump has a pump chamber and at least one pump valve which predefines a delivery direction. The pump chamber preferably has a pump movement imparted to it by a diaphragm or a pump piston. In a preferred embodiment, two pump valves are provided each of which has a passively opening configuration and is respectively disposed upstream or downstream of the pump chamber as viewed in the flow direction of the liquid additive from the tank to the dosing valve.
In a further embodiment, only a single pump valve is provided. The single pump valve is then preferably provided downstream of the pump chamber as viewed in the flow direction. The pump piston is then constructed in such a way that, during a delivery movement (discharge movement), it discharges the liquid additive in the pump chamber through the pump valve. A replenishment flow of liquid additive into the pump chamber then takes place during a return movement of the pump piston directed counter to the delivery movement. A pump of that type is described, for example, in German Patent DE 10 2008 010 073 B4, in particular in FIGS. 2 and 3 and in the explanations with regard thereto in paragraphs [0038] to [0051], the entire content of which is incorporated herein.
The method according to the invention is used, in particular, in the case of a dosing apparatus that preferably does not have a pressure sensor on the pressure accumulator for electronically monitoring the pressure in the pressure accumulator. In this case, the pressure in the pressure accumulator is set exclusively by using the return valve. The return valve preferably acts mechanically.
With the objects of the invention in view, there is concomitantly provided a motor vehicle, comprising an internal combustion engine, an exhaust-gas treatment apparatus for purifying exhaust gases of the internal combustion engine and a dosing apparatus through which a liquid additive can be fed to the exhaust-gas treatment apparatus and which is set up and constructed for operation in accordance with the described method. The motor vehicle is preferably a passenger motor vehicle or a truck. The internal combustion engine is preferably a diesel internal combustion engine. The exhaust-gas treatment apparatus preferably has an SCR catalytic converter for carrying out the method of selective catalytic reduction. The exhaust-gas treatment apparatus is preferably fed with reducing agent, and in particular urea-water solution as a liquid additive, upstream of the SCR catalytic converter. Then, the method of selective catalytic reduction is performed with the reducing agent in the exhaust-gas treatment apparatus for the purpose of reducing nitrogen oxide compounds in the exhaust gas in an effective manner.
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 method for operating a dosing apparatus and a motor vehicle having a dosing apparatus, 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 to the figures of the drawings in detail and first, particularly, to
The structural variant of a dosing apparatus according to
| Number | Date | Country | Kind |
|---|---|---|---|
| 102012002059.7 | Feb 2012 | DE | national |
This is a continuation application, under 35 U.S.C. §120, of copending international application PCT/EP2013/052044, filed Feb. 1, 2013, which designated the United States; this application also claims the priority, under 35 U.S.C. §119, of German patent application DE 10 2012 002 059.7, filed Feb. 3, 2012; the prior applications are herewith incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2013/052044 | Feb 2013 | US |
| Child | 14450423 | US |
