EP2150687A1

EP2150687A1 - Metering system and method for operating a metering system

Info

Publication number: EP2150687A1
Application number: EP07846946A
Authority: EP
Inventors: Frank Noack
Original assignee: Eberspaecher Unna GmbH and Co KG
Current assignee: Eberspaecher Unna GmbH and Co KG
Priority date: 2006-12-22
Filing date: 2007-12-01
Publication date: 2010-02-10
Also published as: WO2008080477A1; DE102006060838A1

Abstract

The invention relates to a metering system for metering a liquid in an exhaust pipe which is connected to an internal combustion engine of a motor vehicle, and to a method for operating a metering system. A metering system (1) is proposed which comprises a storage tank (3) for the liquid, a metering valve (4) for the liquid, a liquid pump (10), and a supply pipeline (12) for supplying the liquid to the metering valve (4). The metering system (1) furthermore has a switchable venting valve (13) which is connected to the supply pipeline (12) and with which it is possible to switch from a metering mode to a venting mode. The venting valve (13) allows the supply pipeline (12) to be vented. According to the invention, in the venting mode a displacement of liquid present in the supply pipeline (12) is brought about by atmospheric air following the activation of the liquid pump (10).

Description

Dosing system and method for operating a dosing system

The invention relates to a metering system for metering a liquid in an exhaust pipe, which is connected to an internal combustion engine of a motor vehicle and a method for operating a metering system according to the preambles of the independent claims.

It is known to introduce for the reduction of nitrogen oxides in the exhaust gas of motor vehicles as a reducing agent, a liquid containing ammonia via a metering system in the exhaust stream, which converts the nitrogen oxides into harmless components. The reducing agent is present, for example, as an aqueous urea solution and releases ammonia only for the catalytic conversion of the nitrogen oxides on contact with the hot exhaust gas flow. In contrast to ammonia, the aqueous urea solution can be easily stored in the vehicle. However, at low temperatures there is the problem that the aqueous urea solution freezes and the metering system is damaged by the freezing volume of the reducing agent with its significant volume increase compared to the liquid state.

Systems are known in which the metering system is heated in order to avoid ice formation. Furthermore, systems are known in which when switching off the combustion motor, the lines of the dosing system are filled with ambient air.

For example, DE 101 50 518 C1 discloses reducing agents via a reducing agent line into a mixing chamber of the metering system, forming a mixture of reducing agent and air, which is supplied to the exhaust gas via a mixture line and a metering valve. After switching off the internal combustion engine, air is further introduced into the mixing chamber and a bypass line bypassing the reducing agent pump is opened, so that the mixing chambers, the mixture line, the metering valve and the reducing agent line are filled with air.

From DE 44 32 577 Al a device is known in which the lines of the metering system are filled after stopping the engine with pressurized ambient air. For this purpose, a Rückspulventil is provided, with which the reducing agent can be rewound into a storage tank or can be spooled out of the metering valve.

DE 102 54 981 A1 also discloses replacing the reducing agent with air after switching off the internal combustion engine from the lines of the metering system. The air is optionally introduced either towards the mixing chamber or in the direction of a storage tank.

The object of the invention is to provide a metering system and a method for operating a metering system with which its antifreeze protection is improved and which can also be used in so-called airless metering systems.

The object is achieved according to the invention by the features of the independent claims. Favorable refinements and further developments of the invention can be taken from the further claims.

The inventive dosing system for dosing a liquid has a storage tank, a Flussigkeitspumpe with Verdrangersystem, a metering valve and a supply line, via which the liquid from the storage tank to the metering valve can be required on. Furthermore, a switchable ventilation valve connected to the supply line is provided, with which it is possible to switch from a metering mode of the metering system into a ventilation mode. In metering mode, the venting valve establishes a flow connection between the fluid pump and the metering valve. In the aeration mode, the breather valve allows for aeration of the supply line, causing a displacement of ambient liquid in the supply line due to actuation of the liquid pump. The metering mode is thus the normal operating mode in which a metering of the liquid is provided or the metering system is in metering readiness. By contrast, the aeration mode is an operating mode in which it is preferable to switch over after the dosing mode has ended so as to at least partially aerate the dosing system. Preferably, the aeration mode is set before stopping the dosing system.

For the purposes of the invention, aeration means an at least partial, but preferably at least approximately complete, replacement of the ammonia-containing liquid by a gaseous displacement medium, preferably ambient air. Preferably, in a process for stopping the metering system, starting from the normal operation in the metering mode, in which the liquid is metered, or at least one Dosierbereitschaft is given in the Switched ventilation mode and at least the supply line vented. As a result, damage to the supply line is avoided, which could occur by volume expansion during freezing of the liquid, in particular when the dosing system is stopped.

The metering system according to the invention has the advantage that for the ventilation of the supply line no separate Fordereinheit for the aeration medium is needed, since the ventilation is effected by the already existing Flussigkeitspumpe. The ventilation medium is ambient air. This eliminates the provision of a compressed air reservoir to displace the liquid during venting. The metering system according to the invention is therefore particularly suitable for so-called air-free metering systems, in which the liquid to be metered is injected into the exhaust gas while dispensing with atomization assisted by compressed air. However, it can also be used in so-called air-assisted dosing systems. The metering system according to the invention is particularly suitable for metering aqueous urea solution as a selective nitrogen oxide reducing agent, but it can also be used for metering other liquids, in particular aqueous, ammonia containing liquids in free or bound form.

In an embodiment of the invention, the Verdrangersystem the Flussigkeitspumpe remains filled in the aeration mode with the liquid substantially. The metering system is preferably designed such that frost damage can not occur in the liquid pump. This is preferably ensured by a frost-proof execution of the liquid pump. As a result of the even after the ventilation process of the dosing system liquid-filled Verdrangersystems the Liquid pump is a trouble-free re-commissioning of the dosing system allows, as immediately the full suction of the liquid pump is available. The displacer system of the fluid pump is preferably formed from a diaphragm chamber or from cylinders into which it is sucked in as a result of a pump actuation or from which it is pressed out.

In a further embodiment of the invention, a return line is provided, via which the liquid can flow back from the metering valve to the storage tank in the metering mode, wherein the return line can be ventilated in the aeration mode. In this way, frost protection is ensured even for the return line. In this case, a partial ventilation of the return line may be sufficient. In particular, in the case of a divided into sections return line under their ventilation to understand that one or more sections are vented.

In a further embodiment of the invention, a suction line is provided, via which the liquid can be sucked out of the storage tank in the metering mode, wherein in the ventilation mode, the suction line remains substantially filled with the liquid. To avoid frost damage, the intake pipe is preferably designed frost-proof. This can be achieved by a flexible or stretchable execution or by volume compensation elements. On aeration of the intake can therefore be omitted in this embodiment.

In a further embodiment of the invention, a drain line is provided, via which a liquid volume displaced in the aeration mode can flow back to the storage tank. The drain line is preferably one separate line, which is used exclusively in ventilation mode. It can therefore be cost-effective, for example in the form of a plastic line.

In a further embodiment of the invention, the supply line and / or the return line are designed to be at least partially hydraulically rigid. In particular, in the case of subdivided lines may be provided to execute one or more of the sections hydraulically rigid. Preferably, the line sections are hydraulically rigid, which can be filled with a standing under an increased dosing liquid pressure. This execution enables a high dosing accuracy of the liquid preferably present in the dosing mode under an overpressure in the supply line and / or the return line. On the other hand, the ventilation of the unyielding or hydraulically rigid line (s) prevents their damage by frost effect.

The inventive method for operating a metering system for metering a liquid is characterized in that the ventilation of a liquid keitsfuhrenden in metering line is effected by the operation of a Flussigkeits- pump, which required the liquid from a storage tank to a metering valve during metering mode of the metering becomes. The ventilation takes place by displacement of the liquid, preferably by ambient air. This is achieved by empty suction of the line to be ventilated, wherein access of ambient air to the line to be ventilated is made possible by actuation of a ventilation valve. At the same time, a flow connection of the other end of the line is established with a suction inlet of the fluid pump. Aeration by impressions of Ambient air in the relevant line by operating the Flussigkeitspumpe is of course also possible.

In an embodiment of the method, a Verdrangersystem the Flussigkeitspumpe remains filled with the liquid in the aeration mode substantially. This procedure is particularly advantageous in the case of empty suction of the line to be ventilated, since a high suction effect can be achieved as a result of the fluid-filled liquid pump.

Advantageous embodiments of the invention are illustrated in the drawings and described below. In this case, the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination of features, but also in other combinations or alone, without departing from the scope of the present invention.

Showing:

Fig. 1 is a schematic representation of an advantageous

Embodiment of the inventive dosing in Dosiermodus and

A schematic representation of an advantageous

Embodiment of the metering system according to the invention in the aeration mode.

The dosing system 1 shown in the dosing mode in FIG. 1 comprises a pump unit 2 for requesting a liquid stored in a storage tank 3 to a metering valve 4, from which it can be injected into a not shown exhaust pipe of an internal combustion engine of a motor vehicle waiving a Druckluftunterstut- tion , The Liquid contains ammonia in free or bound form and is used for selective nitrogen oxide reduction on a catalyst arranged in the exhaust gas line. Preferably, it is an aqueous urea solution, hereinafter referred to simply as HWL. Preferably, the components arranged within the dashed line, explained in more detail below, are combined to form a compact dosing module D.

In the dosing mode of the dosing system shown in FIG

I sucks the pump unit 2 HWL from the storage tank 3 via a suction line 5 at. For this purpose, a changeover valve 6 establishes a flow connection from the suction line 5 to a suction-side connection 7 of the pump unit 2. In this case, by means of a filter 9 arranged in a first connecting line 8 between change-over valve 6 and pump unit 2, a removal of possibly present, in particular particulate impurities, takes place.

A fluid pump 10 provides aspirated HWL at an increased pressure at a pressure port 11 of the pump unit 2. In this case, the liquid pump 10 is preferably designed as a variable in its Forderrate adjustable electrical metering pump in reciprocating or diaphragm pump design. Through a supply line 12 HWL can be required by the pump unit 2 to the metering valve 4. A ventilation valve 13 connected to the supply line 12 provides a flow connection between the pressure connection in the metering mode for this purpose

II and the metering valve 4 ago. For the metering valve 4 required, but not metered into the exhaust HWL can flow back into the storage tank 3 via a return line with a first section 14 and a second section 14 'and further via the switching valve 6 and a second connecting line 15 connected thereto. The metering valve 4 is present preferably formed as a spring-loaded nozzle with an outwardly opening nozzle needle. To deliver HWL into the exhaust gas, a dosing pressure exceeding the corresponding spring force is necessary, which is applied by the fluid pump 10. The dispensing pressure is preferably set so high that no bubble formation by boiling in the supply line 12 also occurs at a 100 ⁰ C heated HWL. A metering pressure in the range of 4 bar to 10 bar is preferred.

A switchable, in particular clocked, operable proportional valve 16 is used in the return line, which can be controlled in connection with the liquid pump 10 so that the provided HWL metering can be discharged into the exhaust. To achieve the greatest possible dosing accuracy or reproducibility sensors are provided in particular for the pump unit 2, which provide information about the relevant pressure and Temperaturverhaltnisse. By way of example, a pressure sensor 17 for the pump output-side HWL pressure and temperature sensors 18, 19 for the pump-inlet-side HWL temperature or the temperature of the drive motor of the fluid pump 10 are shown. With these sensors can be detected and taken into account on the metering accuracy influencing pressure and temperature conditions of the pump unit 2. If required, additional sensors can be provided to detect additional variables influencing the metering accuracy.

In order to avoid a reduction of the dosing accuracy due to pressure-related volume changes, it is provided, in particular supply line 12 and / or the return line at least partially hydraulically rigid execute. Preferably, a hydraulically rigid execution is less least provided for both the supply line 12 and the first portion 14 of the return line, as in these parts of the line in dosing an increased dosing occurs. As a result of the hydraulically rigid execution, a pressure which detrimentally affects the metering accuracy is avoided in the case of pressure changes in these line parts., However, at low temperatures, damage may occur due to freezing, particularly with these line parts, if they are filled with HWL. at least to ventilate the supply line 12, but preferably also the first section 14 of the return line 14, when the metering mode is terminated and the metering system 1 is stopped It may be provided to ventilate also further line parts, such as the second section 14 'of the return line. It is thus provided to switch over before stopping the dosing system 1 in a subsequently explained with reference to FIG. 2 Beluftungs- mode.

To switch to the aeration mode, the ventilation valve 13 is actuated in such a way that, on the one hand, the supply line is connected on the output side to an air inlet 21 of the ventilation valve 13. On the other hand, the pressure port 11 of the pump unit 2 is connected to a discharge pipe 20 led to the storage tank 3. Furthermore, in the case of a clocked proportional valve 16, this is switched to currentless and thus to passage. Furthermore, the switching valve 6 is operated such that the return passage 14 is now brought into flow communication with the suction-side port 7 of the pump unit 2. At the same time, the suction pipe 5 is stromungsmaßig separated from the suction-side terminal 7 of the pump unit 2. As a result of these switches, actuation of the liquid pump 10 causes ambient air to be drawn into the supply line 12. In this way, the supply line 12 is vented, ie in her existing HWL is displaced by the intake ambient air. The displaced HWL volume can flow back into the latter as a result of the flow connection between pressure connection 11 and storage tank 3 produced by switching over the discharge line 20.

The aeration mode is preferably maintained until at least the supply line 12 is vented. This is the case when the previously existing HWL is almost completely empty from it, ie. was displaced by ambient air. Preferably, a ventilation of at least the first portion 14 of the return line is provided. Although not absolutely necessary, it is preferably provided that the decanter system of the fluid pump 10 relevant for the HWL requirement remains substantially filled with HWL in the aeration mode. This improves the suction effect and a refilling of the emptied lines at a restart. Likewise, the suction line 5 remains substantially filled with HWL.

Although not preferred, it is also possible to provide aeration of further line parts or components, such as the connecting line 8 and the filter 9, which are liquid-filled in dosing mode.

If the lines or components provided for ventilation are ventilated after a predetermined period of operation in the aeration mode, the liquid pump 10 is switched off. A ventilation that has taken place can also be detected by sensors that may be present and the termination of the ventilation mode can be triggered by them. When the metering system 1 is restarted, it is switched to the metering mode shown in FIG. This is done first exne venting or Wiederbefullung the previously vented lines and components. In order to ensure this, in the case of a clocked proportional valve 16, this initially remains switched to zero-current until the refilling is completed. Subsequently, the actual dosing operation can be resumed.

Claims

claims

1. dosing system for dosing a liquid in an exhaust pipe, which is connected to an internal combustion engine of a motor vehicle, with a storage tank (3) for the liquid, a metering valve (4), with which the liquid can be discharged into the exhaust pipe, a Flussigkeitspumpe ( 10) with a Verdranger- system through which the liquid from the storage tank (3) to the metering valve (4) may be required, a supply line (12) through which the liquid can be supplied to the metering valve (4), and one to the supply line ( 4) connected switchable ventilation valve (13), which can be switched from a dosing of the dosing (1) in a Beluftungs- mode, wherein the ventilation valve (13) in the dosing mode a flow connection between the Flussigkeitspumpe (10) and the metering valve (4 ) and in the aeration mode allows ventilation of the supply line (12), characterized in that in the air As a result of actuation of the liquid pump (10), a displacement of liquid present in the supply line (12) by ambient air is effected.

2. Dosing system according to claim 1, characterized in that in the aeration mode, the displacement system of the liquid pump (10) remains substantially filled with the liquid.

3. Dosing system according to claim 1 or 2, characterized in that a return line (14, 14 ') is provided, via which the liquid from the metering valve (4) can flow back to the storage tank (3) in the metering mode, wherein in the aeration mode, the return line (14 , 14 ') can be ventilated.

4. Dosing system according to one of claims 1 to 3, characterized in that a suction line (5) is provided, via which in the metering mode, the liquid from the storage tank (3) can be sucked, wherein in the ventilation mode, the suction line (5) substantially with the liquid remains filled.

5. Dosing system according to one of claims 1 to 4, characterized in that a discharge line (20) is provided, via which a displaced in the aeration mode liquid volume to the storage tank (3) can flow back.

6. Dosing system according to one of claims 1 to 5, characterized in that the supply line (12) and / or the return line (14, 14 ') are designed at least partially hydraulically rigid.

7. A method for operating a metering system for metering a liquid in an exhaust pipe, which is connected to an internal combustion engine of a motor vehicle, in particular according to one of claims 1 to 6, wherein one in a metering mode for the metering system

(1) flussigkeitsfuhrende line is ventilated, characterized in that the ventilation of the line by the operation of a

Flussigkeitspumpe (10) is effected, by which at

Dosing mode of the dosing (1) the liquid from a storage tank (3) to a metering valve (4) is required.

8. The method according to claim 7, characterized in that in the aeration mode a Verdrangersystem the Flussigkeitspumpe (10) with the liquid remains substantially filled.