DE102012002059A1 - Method for operating a metering device - Google Patents

Abstract

The invention relates to a method for operating a metering device (1) for providing a liquid additive. The metering device has at least at least one pump (2) for conveying the additive from a tank (3) into an accumulator (4), a metering valve (5), which is adapted to provide metered in the pressure accumulator (4) present additive, and a return valve (6) through which in the pressure accumulator (4) present additive can be discharged back into the tank (3) on. In the method, a dosing request is first determined in a step a). Subsequently, in a step b), the pump (2) is activated in order to build up a pressure in the pressure accumulator (4). Then, the pressure in the pressure accumulator (4) is set to a desired metering pressure (8). Thereupon, in a step d), the liquid additive is discharged through the metering valve (5).

Description

The invention relates to a method for operating a metering device for providing a liquid additive. The metering device can be used, for example, to supply a liquid additive into the exhaust gas treatment device, where it is used to clean the exhaust gases of a mobile internal combustion engine (in particular in a motor vehicle).

Exhaust treatment devices, in which a liquid additive is supplied, are finding more and more widespread lately. An exhaust gas purification process which is particularly frequently carried out in such exhaust gas treatment devices is the selective catalytic reduction (SCR) process, in which nitrogen oxide compounds in the exhaust gas are reduced with the aid of a reducing agent. The reducing agent is supplied to the exhaust gas treatment device regularly in the form of a liquid additive. A particularly frequently used in this context, the liquid additive is urea-water solution. A urea-water solution with a urea content of 32.5% is commercially available under the trade name AdBlue ^® and widely used. The urea-water solution is merely a reductant precursor and is exhausted externally (in a dedicated reactor) or converted to ammonia (the reducing agent) internally of the exhaust gas (in the exhaust treatment device under the influence of the exhaust gas). Nitrogen oxide compounds in the exhaust gas are then reduced together with the ammonia in the presence of an SCR catalyst to harmless substances (water, CO ₂ and nitrogen). In particular in this technical field the invention finds application.

The metering device for providing a liquid additive (urea-water solution) should be as simple as possible, as long-term stable and maintenance-free and inexpensive. At the same time, it is desired that the metering accuracy of a metering device is particularly high. As a result, on the one hand, the amount of liquid additive necessary for the conversion of pollutant constituents in the exhaust gas can be set particularly precisely. In addition, it is possible to effectively avoid overdoses.

On this basis, it is an object of the invention to solve the problems described in connection with the prior art, or at least alleviate. In particular, a particularly advantageous method for operating a metering device for urea-water solution will be presented.

These objects are achieved by a method according to the features of claim 1. Further advantageous embodiments of the invention are specified in the dependent formulated claims. The features listed individually in the claims are combinable with each other in any technologically meaningful manner and can be supplemented by explanatory facts from the description, wherein further embodiments of the invention are shown.

The invention relates to a method for operating a metering device for providing a liquid additive, in particular urea-water solution.

• – mindestens eine Pumpe zur Förderung des Additivs aus einem Tank in einen Druckspeicher,
• – ein Dosierventil, welches dazu eingerichtet ist, in dem Druckspeicher vorliegendes Additiv dosiert bereitzustellen, und
• – ein Rücklaufventil, durch welches in dem Druckspeicher vorliegendes Additiv zurück in den Tank abgeleitet werden kann.

The metering device has at least the following:

• At least one pump for conveying the additive from a tank to an accumulator,
• A metering valve, which is adapted to provide metered in the accumulator additive present, and
• - A return valve through which existing in the pressure accumulator additive can be derived back into the tank.

• a) Feststellen einer Dosieranforderung,
• b) Aktivieren der Pumpe, um einen Druck in dem Druckspeicher aufzubauen,
• c) Einstellen des Drucks in dem Druckspeicher auf einen Dosierdruck, und
• d) Abgabe des Additivs durch die Dosiervorrichtung.

The method comprises at least the following steps:

• a) determining a dosing request,
• b) activating the pump to build up a pressure in the accumulator,
• c) adjusting the pressure in the accumulator to a metering pressure, and
• d) delivery of the additive through the metering device.

The metering device is particularly preferably used for metering a reducing agent (or a reducing agent precursor such as urea-water solution) as a liquid additive in an exhaust treatment device 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 no electronic control or control is provided, with which the amount of additive pumped by the pump can be precisely determined. The tank is preferably connected to the pump via a suction line, via which the pump can suck in liquid additive from the tank. The pressure accumulator is preferably arranged in a flow direction of the liquid additive from the tank to the metering valve behind the pump. A pressure built up by the pump is present in the pressure accumulator. The pressure accumulator may for example be designed as a flexible conduit which expands as soon as liquid additive under pressure from the pump into the flexible conduit is encouraged. The metering valve is preferably an electrically controlled solenoid valve which can be opened and closed by the electric drive, wherein the opening time of the metering valve dictates the amount of liquid additive provided. At the accumulator also adjoins a return valve. The return valve is preferably connected via a return line back into the tank, so that in the pressure accumulator present liquid additive can be discharged back into the tank.

When determining a dosing request in step a) an electronic signal of a motor control is preferably identified, which is representative of a Dosieranforderung. For example, a motor controller sends out a signal that corresponds to a certain amount of liquid additive needed. This signal is detected or identified as Dosieranforderung. During step a), a pressure which is so low that processing of the dosing request is not possible is preferably present in the pressure reservoir. Preferably, the pressure in the pressure accumulator during step a) is below 2 bar, more preferably below 1 bar and most preferably below 0.5 bar. In step b), the pump is activated in order to build up a pressure in the accumulator, which is necessary for a suitable metering with the metering valve. 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 necessary to build up the necessary pressure in the accumulator depends on the flexibility of the accumulator and on the pressure difference between the pressure during step a) and the metering pressure (step b). The more flexible the pressure accumulator, the more liquid additive can be conveyed into the pressure accumulator so that the necessary pressure is built up. The greater the pressure difference, the more liquid additive can be conveyed into the pressure accumulator. The pressure built up by the activation of the pump in step b) is preferably between 3 and 10 bar, more preferably between 5 and 10 bar and most preferably between 6 and 8 bar. The pressure built up by the pump in step b) is typically slightly above the dosing pressure necessary to accurately meter with the dosing valve. This is because the pump is preferably unregulated. This means that the pump is not deactivated when a certain pressure is reached, but after an activation the pump initially continues to run, regardless of how high the pressure acting in the pressure accumulator is against the pump.

In one embodiment variant of the described method, the pump stops its operation only when the pressure in the pressure accumulator is so great that the pump can no longer generate any further pressure increase in the pressure accumulator.

The method is particularly preferred if the method steps a) to d) are carried out repeatedly during the operation of the metering device. Furthermore, the method is preferred if, for setting the pressure in step c), the pressure is reduced, in particular in which the return valve is opened. In order to set a precise pressure in the pressure accumulator, which is desired in order to be able to carry out a very accurate metering with the metering valve, the return valve is therefore preferably opened.

During step c), step b) preferably continues to take place. The return valve remains open and the pump is activated. By a return flow of liquid additive through the return valve, the pressure in the accumulator remains constant.

In addition, the method is preferred if at least steps c) and d) at least partially run parallel to each other. Even more preferably, even steps b), c) and d) take place at least partially in parallel (at the same time).

To discharge the liquid additive through the metering valve in step d), the metering valve is opened. Then liquid additive flows from the pressure accumulator through the metering valve to a consumer for the liquid additive. The consumer of the liquid additive is preferably an exhaust gas treatment device in which the selective catalytic reduction process is carried out with the liquid additive. During the execution of step d), the process steps b) and c) preferably continue to take place. During step d), the pump continues to be activated and continues to deliver liquid additive into the accumulator. The return valve is also preferably open during step d) and ensures that the pressure in the pressure accumulator is adjusted to the dosage pressure of, for example, a value between 5 and 10 bar, for example 7 bar, necessary for metering. The return valve is preferably not always open, but it is opened under pressure control, respectively, as soon as the pressure in the accumulator exceeds the metering pressure. As a result, the pressure in the pressure accumulator is always adjusted during dispensing of the additive through the metering valve to the metering pressure.

When the additive is dispensed in step d), it is not necessary for the metering valve to be open all the time. It is also possible that the dosing request determined in step a) is delivered in several pulses. One pulse corresponds in each case an opening operation and a closing operation of the metering valve.

If the method is carried out repeatedly during the operation of the metering device, it is preferable after step d) in each case to deactivate the pump. The pump is then activated again only when a new dosing request is detected in a new step a). The pump runs in particular during operation of a delivery line and a motor vehicle in which the metering device is arranged, not continuously, but the pump is regularly activated only when a Dosieranforderung is present.

• e) Absenken des Drucks in dem Druckspeicher.

Furthermore, the method is advantageous if the following method step is carried out after method step d):

• e) lowering the pressure in the accumulator.

The process step e) is preferably carried out repeatedly together with the process steps a) to d).

By lowering the pressure in the pressure accumulator in step e) it is possible to the accumulator between two dosing requirements. relieve. As a result, the durability of the metering device can be increased. The discharge of the accumulator can be actively carried out in a variant embodiment. A return valve, which branches off from the pressure accumulator, may optionally be opened actively in step e) in order to allow the liquid additive to escape from the pressure accumulator and thus to ensure a lowering of the pressure in the pressure accumulator. This return valve can be identical to the return valve used in step c) of the method and have an additional possibility for active opening in step e). But it is also possible that an additional return valve is provided for step e), which can be actively opened, and is preferably arranged in a parallel second return line from the pressure accumulator to the tank.

According to a further embodiment variant of the method, it is also possible that an active discharge takes place through the pump of the delivery unit. The pump may optionally be operated counter to the conveying direction in step e) in order to convey liquid additive out of the accumulator back into the tank, so that the pressure in the pressure accumulator decreases and the pressure accumulator is relieved.

It is also possible that a passive discharge of the pressure accumulator takes place. For this purpose, by a return valve and / or by the pump in step e) a Lekagestrom flow of liquid additive back into the tank, through which the pressure in the pressure accumulator lowers. With a passive discharge in step e), the pressure in the pressure accumulator decreases comparatively slowly, because the leakage flow is regularly relatively small. Otherwise, the effect of the leakage flow on the pressure in the pressure accumulator would be too great during the dosing in step d).

In addition, the method variant is considered advantageous if the return valve is a passively opening valve whose opening pressure corresponds to the metering pressure.

The return valve is preferably a passively-opening valve which opens at a predetermined or preset limit pressure, which limit pressure corresponds to the metering pressure (the pressure with which the additive is metered in). The return valve preferably has a valve body and a valve spring which biases 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 such a return valve allows a particularly cost-effective metering device, because no (electric) drive for the metering valve and no control unit to control the return valve is necessary.

The metering device can be designed without an electrically driven metering valve and / or without an (active) control unit of the return valve.

In addition, the method is advantageous when the return valve is an actively opening valve with a valve drive, wherein the pressure accumulator, a pressure sensor is arranged and the return valve is controlled by means of the valve drive from a control unit to in step c) the pressure in the pressure accumulator to set to the desired metering pressure.

The valve drive may, for example, be an electromagnet, which exerts a force on an armature in the return valve, by means of which the return valve can be opened and / or closed. The pressure sensor can be embodied, for example, as an electronic pressure sensor which measures a pressure in the pressure accumulator and transmits it as an electrical signal to the control unit. This pressure information is then processed in the control unit to specify whether the return valve is opened and / or closed (control loop).

Also advantageous is the method when the pump has a pump chamber and at least one pump valve, which has a conveying direction pretends. The pump chamber is preferably acted upon by a diaphragm or a pump piston with a pump movement. In a preferred embodiment, two pump valves are provided, which are each passively opening and are arranged in the flow direction of the liquid additive from the tank to the metering valve in front of and behind the pump chamber.

In another embodiment, only a single pump valve is provided. This single pump valve is then preferably provided in the flow direction behind the pump chamber. The pump piston is then adapted to push out the liquid additive in the pump chamber through the pump valve during a delivery movement (ejection movement). In one of the conveying movement directed backward movement of the pump piston then liquid additive flows into the pump chamber. Such a pump is, for example, in the DE 10 2008 010 073 B4 , especially in the 2 and 3 as well as the explanations on this in paragraphs [0038] to [0051], to which reference should be made in full here.

The inventive method finds particular application in a metering device, which preferably has no pressure sensor on the pressure accumulator, with which the pressure in the pressure accumulator is electronically monitored. The pressure in the accumulator is set in this case alone by the return valve. The return valve preferably acts mechanically.

The invention also applies to a motor vehicle, comprising an internal combustion engine, an exhaust gas treatment device for cleaning the exhaust gases of the internal combustion engine and a metering device, with which the exhaust gas treatment device, a liquid additive can be supplied, and which is set up and designed for operation according to the described method. The motor vehicle is preferably a passenger car or a truck. The internal combustion engine is preferably a diesel internal combustion engine. The exhaust treatment device preferably comprises an SCR catalyst for carrying out the selective catalytic reduction process. As a liquid additive, the exhaust treatment device is preferably supplied with reducing agent and, in particular, urea-water solution upstream of the SCR catalyst. With the reducing agent, the method of selective catalytic reduction is then performed in the exhaust gas treatment apparatus to effectively reduce nitrogen oxide compounds in the exhaust gas.

The invention and the technical environment will be explained in more detail with reference to FIGS. The figures show particularly preferred embodiments, to which the invention is not limited. In particular, it should be noted that the figures and in particular the illustrated proportions are only schematic. Show it:

1 a metering device together with a tank and an exhaust gas treatment device,

2 a further embodiment of a metering device together with a tank and an exhaust gas treatment device

3 : a motor vehicle having a metering device,

4 : a first diagram of the sequence of the method according to the invention, and

5 : a second diagram of the sequence of the method according to the invention.

1 shows a metering device 1 together with a tank 3 and an exhaust treatment device 11 , The dosing device 1 takes the tank 3 Liquid additive (urea-water solution) at a sampling point 17 , From the sampling point 17 starting a delivery line extends 18 , which first to a pump 2 runs. Starting from the pump 2 extends the delivery line 18 continue to a metering valve 5 with which the liquid additive in an exhaust gas flow 13 in the exhaust treatment device 11 can be supplied. The liquid additive is due to the pumping action of the pump 2 from the tank 3 through the support line 18 to the metering valve 5 promoted. In the conveying direction from the tank 3 to the metering valve 5 behind the pump 2 there is a pressure accumulator 4 , The accumulator 4 can be partially from the delivery line 18 be formed, for example, characterized in that the delivery line 18 is designed as a flexible hose. From the accumulator 4 starting a return line branches 12 off, which back into the tank 3 leads. In the return line 12 is a return valve 6 arranged. With such a metering device, the inventive method can be carried out in a particularly advantageous manner.

The embodiment of a metering according to 2 is largely consistent with the embodiment according to 1 match. In addition, here is a valve drive 19 provided with which the return valve 6 can be opened and closed. To the accumulator 4 is adjacent to a pressure sensor 20 with which the pressure in the accumulator 4 can be measured. The pressure information associated with the pressure sensor 20 is determined, arrives at a control unit 21 and is processed there. The control unit 21 can the return valve 6 With Help of the valve drive 19 open and close as needed.

3 shows a motor vehicle 9 comprising an internal combustion engine 10 and an exhaust treatment device 11 , with which the exhaust gases of the internal combustion engine 10 can be cleaned. The exhaust gases of the internal combustion engine 10 flow through as exhaust gas flow 13 the exhaust treatment device 11 , At the exhaust treatment device 11 is a metering valve 5 provided with which a liquid additive in the exhaust treatment device 11 can be supplied. The metering valve 5 is from a dosing device 1 with liquid additive from a tank 3 provided.

4 shows a first flowchart of the method according to the invention. To recognize is the time axis 14 and the pressure axis 15 of the diagram. About the time axis 14 is a pressure gradient 16 applied during the process according to the invention. The pressure gradient 16 is representative of the pressure in the accumulator of the described metering device. In step a), the pressure in the pressure accumulator is at a low, constant rest pressure level, which is, for example, less than 2 bar. During step a), a dosing request is detected. If a dosing request has been detected, in step b) the activation of the pump increases the pressure in the pressure reservoir as described above. The pressure gradient 16 rises strongly. In step b), the pressure is partially increased so much that this is a metering pressure 8th exceeds. By opening the return valve in step c), the pressure on the metering pressure 8th set as described above. Then in step d) a discharge of the liquid additive through the metering valve, wherein the liquid additive the metering pressure 8th having. Subsequently, step e) is carried out, in which the pressure in the pressure accumulator drops again. The pressure gradient 16 is preferred back to the resting pressure 7 from step a) reduced. An active implementation of step e) (for example by an active opening of a return valve or a return pumping by means of the pump) is not necessary. It is also sufficient if the pressure in step e) passively drops (for example due to a leakage flow through a return valve or through the pump).

In 5 the process steps a), b), c), d) and e) are shown again. It can be seen that the method steps are carried out regularly in the manner of a loop.

LIST OF REFERENCE NUMBERS

1

metering

2

pump

3

tank

4

accumulator

5

metering valve

6

Return valve

7

resting pressure

8th

dosing pressure

9

motor vehicle

10

Internal combustion engine

11

Exhaust treatment device

12

Return line

13

exhaust gas flow

14

timeline

15

pressure axis

16

pressure curve

17

sampling point

18

delivery line

19

valve drive

20

pressure sensor

21

control unit

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102008010073 B4 [0029]

Claims (9)

Method for operating a metering device ( 1 ) for providing a liquid additive, at least comprising at least one pump ( 2 ) for conveying the additive from a tank ( 3 ) in an accumulator ( 4 ), a metering valve ( 5 ), which is adapted to be stored in the accumulator ( 4 ) present metered additive, and a return valve ( 6 ), through which in the accumulator ( 4 ) present additive back into the tank ( 3 ), the method comprising at least the following steps: a) determining a dosing request; b) activating the pump ( 2 ) to a pressure in the accumulator ( 4 ) to build up; c) adjusting the pressure in the accumulator ( 4 ) to a metering pressure ( 8th ); and d) dispensing of the additive through the metering valve ( 5 ). Method according to claim 1, wherein the method steps a) to d) during the operation of the metering device ( 1 ) are performed repeatedly in the manner of a loop. Method according to one of the preceding claims, wherein for adjusting the pressure in step c) the return valve ( 6 ) is opened. Method according to one of the preceding claims, wherein at least steps c) and d) at least partially run parallel to each other. Method according to one of the preceding claims, wherein after method step d) the following method step is carried out: e) lowering the pressure in the pressure accumulator ( 4 ). Method according to one of the preceding claims, wherein the return valve ( 6 ) is a passively opening valve whose opening pressure corresponds to the metering pressure. Method according to one of the claims 1 to 5, wherein the return valve ( 6 ) an actively opening valve with a valve drive ( 19 ), wherein at the accumulator ( 4 ) a pressure sensor ( 20 ) is arranged and the return valve ( 6 ) by means of the valve drive ( 19 ) from a control unit ( 21 ) is controlled in step c) the pressure in the accumulator ( 4 ) to the dosing pressure ( 8th ). Method according to one of the preceding claims, wherein the pump ( 2 ) a pump chamber ( 7 ) and at least one pump valve ( 8th ), which has a conveying direction ( 12 ) pretends. Motor vehicle ( 9 ), comprising an internal combustion engine ( 10 ), an exhaust treatment device ( 11 ) for cleaning the exhaust gases of the internal combustion engine ( 10 ) and a metering device ( 1 ), with which the exhaust gas treatment device ( 11 ) a liquid additive can be supplied, and which is designed and designed for operation by a method according to one of the preceding claims.

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