DE102006060838A1 - Equipment dosing reductant fluid into automobile exhaust system, is designed to vent lines, replacing liquid by ambient air to prevent frost damage - Google Patents

Abstract

When in the venting mode, pump (10) operation causes liquid in the supply line (12) to be displaced by ambient air. In this mode the pump remains largely liquid-filled. In the dosing mode, fluid can return back to the storage tank (3) via a return line (14, 14'), from the dosing valve (4). In the venting mode, the return line can be vented. A suction line (5) extracts fluid from the storage tank in the dosing mode. In the venting mode, this line remains largely full. An independent claim IS INCLUDED FOR the corresponding method of operation.

Description

The The invention relates to a metering system for metering a liquid in an exhaust pipe connected to an internal combustion engine of a motor vehicle and a method of operating a metering system according to the Topics of the independent Claims.

It is known for the reduction of nitrogen oxides in the exhaust of motor vehicles as reducing agent, an ammonia-containing liquid via a Introduce metering in the exhaust stream, which is the nitrogen oxides in harmless Converts components. The reducing agent is for example as watery urea solution before and uses ammonia only for the catalytic conversion of nitrogen oxides in contact with the hot Exhaust gas flow free. In contrast to ammonia, the aqueous urea solution can be formed stock a simple way in the vehicle. However, there are deep ones Temperatures the problem that the aqueous urea solution freezes and the dosing system by the frost volume of the reducing agent with its considerable in comparison with the liquid state Volume increase damaged becomes.

It Systems are known in which a heating of the metering system takes place to avoid ice formation. Furthermore, there are systems known, in which when stopping the combus- tion motor, the lines the dosing be filled with ambient air.

So revealed the DE 101 50 518 C1 To inject reducing agent via a reducing agent line in a mixing chamber of the dosing, wherein a mixture of reducing agent and air is formed, 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 opened a bypass line bypassing the reducing agent, so that the mixing chamber, the mixture line, the metering valve and the reducing agent line are filled with air.

From the DE 44 32 577 A1 is a device bekamt, in which the lines of the dosing are filled after stopping the engine with pressurized ambient air. For this purpose, a backwash valve is provided, with which the reducing agent can be flushed back into a storage tank or flushed out of the metering valve.

Also the DE 102 54 981 A1 discloses replacing the reducing agent with air after stopping 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.

task The invention is the creation of a dosing system and a method for operating a dosing system that improves its antifreeze protection is and also used in so-called airless dosing systems can be.

The The object is achieved by the Characteristics of the independent claims solved.

Favorable price and further developments of the invention are the further claims remove.

The Dosing system according to the invention for dosing a liquid has a storage tank, a liquid pump with displacement system, a metering valve and a supply line via which the liquid can be promoted from the storage tank to the metering valve on. Further is one to the supply line connected switchable ventilation valve provided with which of a dosing of the dosing in a ventilation mode can be switched. In dosing mode, the ventilation valve provides a flow connection between the liquid pump and the metering valve. In ventilation mode allows the ventilation valve a ventilation the supply line, being due to an operation the liquid pump a repression of in the supply line through existing fluid Ambient air is effected. The dosing mode is thus the normal one Operating mode in which a dosage of the liquid is provided or the Dosing system is in Dosierbereitschaft. In the ventilation mode on the other hand, it is a mode of operation, in which preferably Ending the dosing mode is switched to the dosing system at least partially to ventilate. Preferably, the aeration mode is present a shutdown of the dosing set.

Under ventilation is in the sense of the invention an at least partially, preferably but at least approximately complete Replacement of the ammonia-containing liquid by a gaseous displacement medium, preferably ambient air understood. Preferably, in one Process for stopping the dosing system from the normal Operation in dosing mode, in which the liquid is metered, or at least a Dosierbereitschaft is given, switched to the ventilation mode and at least the supply line ventilated. This will cause damage the supply line avoided, which by volume expansion during freezing of the liquid especially when the dosing system is stopped.

The Dosing system according to the invention has the advantage of being for ventilation the supply line no separate conveyor unit for the Ventilation medium is needed because the ventilation through the already existing liquid pump is effected. As ventilation medium serves ambient air. This makes it unnecessary the provision of a compressed air reservoir for the displacement of liquid when ventilating. The metering system according to the invention is therefore in particular for so-called air-free dosing suitable, in which the zu dosing liquid waiving a compressed air assisted nebulization into the exhaust gas injected becomes. However, it can also be used in so-called air-assisted dosing systems be used. The metering system according to the invention is in particular for the dosage of aqueous urea solution however, it may be useful as a selective nitric oxide reducing agent also for dosing other liquids, especially aqueous, Ammonia in free or bound form containing liquids be used.

In Embodiment of the invention remains in the ventilation mode, the displacement system the liquid pump with the liquid essentially filled. The dosing system is preferably designed such that frost damage at the liquid pump can not occur. Preferably, this is due to a frost-proof design of liquid pump guaranteed. As a result of the after the ventilation process of the dosing liquid-filled displacer system the liquid pump allows a trouble-free restart of the dosing system, because the full suction power of the liquid pump is immediately available. The displacer system the liquid pump is preferably formed from a diaphragm chamber or from cylinders, in which it sucked as a result of a pump actuation or from which pushed it out becomes.

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

In Another embodiment of the invention, an intake pipe is provided, via which in dosing mode the liquid can be sucked from the storage tank, 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 by a flexible or stretchable design or by volume compensation elements be achieved. On aeration the suction line can therefore be omitted in this embodiment become.

In Another embodiment of the invention, a drain line is provided, via which one in ventilation mode extruded Liquid volume to Storage tank can flow back.

at the drain line is preferably a separate one Lead, which exclusively in ventilation mode is used. It can therefore cost, for example in shape executed a plastic line be.

In Further embodiment of the invention are the supply and / or the return line at least partially hydraulically rigid executed. Especially may be provided in the case of sections divided into sections be hydraulically rigid perform one or more of the sections. Prefers the line sections are hydraulically rigid, the with one under one elevated Dosing pressure standing liquid be filled can. This execution allows a high dosing accuracy of preferably in dosing under an overpressure in the supply line and / or the return line existing liquid. On the other hand, through the ventilation the unyielding or hydraulically rigid cable (s) whose damage by Frost effect avoided.

The inventive method for operating a dosing system for dosing a liquid is characterized in that the aeration in Dosiermodus fluid-carrying line caused by the operation of a liquid pump becomes, through which the metering mode of the dosing the liquid is conveyed from a storage tank to a metering valve. The ventilation takes place by repression the liquid preferably by ambient air. This is due to empty eyes of the to be ventilated Line reached, whereby by actuation of a ventilation valve an access of ambient air is made possible to the line to be ventilated. At the same time, a flow connection the other end of the line with a suction inlet of the liquid pump produced. Aeration by impressions of ambient air in the relevant line by pressing the liquid pump is natural also possible.

In an embodiment of the method, a displacement system of the liquid pump with the liquid remains substantially filled in the ventilation mode. This procedure is especially with ei Vacuuming the line to be ventilated advantageous because a high suction effect can be achieved due to the liquid-filled liquid pump.

advantageous embodiments The invention is illustrated and illustrated in the drawings described below. Here are the above and to be explained below Features not only in the specified feature combination, but also usable in other combinations or in isolation, without to leave the scope of the present invention.

there demonstrate:

1 A schematic representation of an advantageous embodiment of the metering system according to the invention in dosing and

2 a schematic representation of an advantageous embodiment of the metering system according to the invention in the ventilation mode.

This in 1 in the dosing mode dosing shown 1 includes a pump unit 2 to promote one in a storage tank 3 stored liquid to a metering valve 4 , from which it can be injected waiving a compressed air support in an exhaust pipe, not shown, an internal combustion engine of a motor vehicle. 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 frame, which are explained in more detail below, are combined to form a compact dosing module D.

In the in 1 Dosing mode of the dosing system shown 1 sucks the pump unit 2 HWL from the storage tank 3 via a suction line 5 at. A changeover valve 6 this provides a flow connection from the suction line 5 to a suction-side connection 7 the pump unit 2 ago. In this case, by means of a in a first connection line 8th between changeover valve 6 and pump unit 2 arranged filter 9 a removal of optionally present, in particular particulate impurities.

A liquid pump 10 provides suctioned HWL with an increased pressure at a pressure port 11 the pump unit 2 ready. Here is the liquid pump 10 preferably designed as an adjustable in their delivery rate electric metering pump in reciprocating or diaphragm pump design. Via a supply line 12 can HWL from the pump unit 2 to the metering valve 4 be encouraged. One to the feed line 12 connected ventilation valve 13 In dosing mode, this creates a flow connection between the pressure connection 11 and the metering valve 4 ago. To the dosing valve 4 promoted, but not metered into the exhaust HWL can via a return line with a first section 14 and a second section 14 ' and continue via the switching valve 6 and a second connection line connected thereto 15 back to the storage tank 3 stream. Here is the metering valve 4 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, that of the liquid pump 10 is applied. The metering pressure is preferably set so high that even with a HWL heated above 10 ° C. no formation of bubbles due to boiling in the feed line 12 occurs. A metering pressure in the range of 4 bar to 10 bar is preferred.

In the return line is one of their sections 14 . 14 ' connecting switchable, in particular clocked operable proportional valve 16 used, which in connection with the liquid pump 10 can be controlled so that the proposed HWL metering can be discharged into the exhaust. To achieve the greatest possible dosing accuracy or reproducibility are sensors in particular for the pump unit 2 provided, which provide information about the relevant pressure and temperature conditions. Exemplary are a pressure sensor 17 for the pump output side HWL pressure and temperature sensors 18 . 19 for the pump input side HWL temperature or the temperature of the drive motor of the liquid pump 10 located. These sensors can influence the dosing accuracy of pressure and temperature conditions of the pump unit 2 recorded and taken into account. If required, additional sensors can be provided to detect additional variables influencing the metering accuracy.

In order to avoid a reduction in the dosing accuracy as a result of pressure-related volume changes, it is provided, in particular supply line 12 and / or at least partially execute the return line hydraulically rigid.

Preferably, a hydraulically rigid design is at least for both the feed line 12 as well as for the first section 14 provided the return line, as in these parts of the line in dosing an increased dosing occurs. As a result of the hydraulically rigid design is a dosing accuracy unfavorably influencing "breathing" ver with pressure changes in these parts avoided. At low temperatures, however, it may cause damage due to freezing, especially in these line parts, if they are filled with HWL. According to the invention, therefore, at least the supply line is provided 12 , but preferably also the first section 14 the return line 14 to vent when the dosing mode ends and the dosing system 1 is stopped. It can be provided, also other line parts, such as the second section 14 ' to ventilate the return line. It is thus intended, before stopping the dosing 1 in one below using the 2 to change the ventilation mode explained.

To switch to the ventilation mode, the ventilation valve 13 actuated such that on the one hand the supply line on the input side with an air inlet 21 of the ventilation valve 13 is connected. On the other hand, the pressure connection becomes 11 the pump unit 2 with one to the storage tank 3 guided drainage line 20 connected. Furthermore, in the case of a clocked proportional valve 16 this de-energized and thus switched to passage. Furthermore, the switching valve 6 actuated such that the return line 14 now in flow communication with the suction-side connection 7 the pump unit 2 is brought. At the same time the suction line 5 in terms of flow from the suction side connection 7 the pump unit 2 separated.

As a result of these switching causes actuation of the liquid pump 10 that ambient air into the supply line 12 is sucked. In this way, the feed line 12 ventilated, ie in her existing HWL is displaced by the sucked ambient air. The displaced HWL volume may be due to switching over the drain line 20 established flow connection between pressure port 11 and storage tank 3 to flow back in the latter.

The aeration mode is preferably maintained until at least the supply line 12 ventilated. This is the case when the previously existing HWL has been almost completely emptied out of it, ie has been displaced by ambient air. Preferably, ventilation is also at least of the first section 14 provided the return line. Although not absolutely necessary, it is preferably provided that the decisive factor for the HWL promotion displacement system of the liquid pump 10 remains substantially filled with HWL in the aeration mode. This improves the suction effect and refilling the emptied lines at a restart. Likewise, the suction line remains 5 essentially filled with HWL.

Although not preferred, can also be a ventilation of other, liquid-filled in metering line parts or components, such as the connecting line 8th and the filter 9 be provided.

If the lines or components provided for ventilation are ventilated after a predetermined period of operation in the ventilation mode, the fluid pump becomes 10 switched off. A ventilation that has taken place can also be detected by sensors which may be present and the termination of the ventilation mode can be triggered by them.

When restarting the dosing system 1 this will be in the in 1 switched dosing mode shown. In this case, there is first a venting or refilling the previously vented lines and components. To ensure this, remains in the case of a clocked proportional valve 16 this first switched to passage without current until the refilling is completed. Subsequently, the actual dosing operation can be resumed.

Claims (8)

Dosing system for dosing a liquid in an exhaust pipe, which is connected to an internal combustion engine of a motor vehicle, comprising - a storage tank ( 3 ) for the liquid, - a metering valve ( 4 ), with which the liquid can be discharged into the exhaust pipe, - a liquid pump ( 10 ) with a displacement system, through which the liquid from the storage tank ( 3 ) to the metering valve ( 4 ), - a supply line ( 12 ), via which the liquid to the metering valve ( 4 ), and - one on the supply line ( 4 ) connected switchable ventilation valve ( 13 ), with which of a dosing mode of the dosing ( 1 ) can be switched to a ventilation mode, wherein the ventilation valve ( 13 ) in the dosing mode, a flow connection between the liquid pump ( 10 ) and the metering valve ( 4 ) and in the aeration mode aeration of the supply line ( 12 ), characterized in that in the aeration mode as a result of actuation of the liquid pump ( 10 ) a displacement of in the supply line ( 12 ) existing liquid is caused by ambient air. Dosing system according to claim 1, characterized in that in the ventilation mode, the displacer system of the liquid pump ( 10 ) remains substantially filled with the liquid. Dosing system according to claim 1 or 2, characterized in that a return line ( 14 . 14 ' ) is provided, via which in the metering mode, the liquid from the metering valve ( 4 ) to the storage tank ( 3 ), wherein in the aeration mode, the return line ( 14 . 14 ' ) can be ventilated. 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 ), wherein in the aeration mode, the suction line ( 5 ) remains substantially filled with the liquid. Dosing system according to one of claims 1 to 4, characterized in that a drain line ( 20 ) is provided, via which a displaced in the aeration mode liquid volume to the storage tank ( 3 ) can flow back. 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 executed at least partially hydraulically rigid. Method for operating a metering system for metering a liquid into 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, in which one in a metering mode for the metering system ( 1 ) is vented liquid-conducting line, characterized in that the ventilation of the line by the operation of a liquid pump ( 10 ) is effected, by which in the dosing of the dosing ( 1 ) the liquid from a storage tank ( 3 ) to a metering valve ( 4 ). A method according to claim 7, characterized in that in the ventilation mode, a displacement system of the liquid pump ( 10 ) remains substantially filled with the liquid.