DE102009029247A1 - Method for conveying reducing medium from storage tank, involves detecting low liquid level in storage tank and preparing pole reversal of conveying device - Google Patents

Abstract

The method involves detecting a low liquid level (72) in a storage tank (12), preparing a pole reversal of a conveying device (42) during positioning a vehicle and opening a dosing module (52) of a dosing system. Volumes (62) are provided, which are transferred due to the effect of the hydrostatic pressure.

Description

State of the art

DE 10 2006 027 487 A1 discloses a vehicle tank for a liquid reducing agent, in particular for a urea solution. A storage tank for a liquid, for example aqueous, reducing agent, in particular for a urea solution for reducing nitrogen oxides in the exhaust gas of internal combustion engines, is disclosed. The vehicle tank has a container wall which is made of plastic. Preferably, the entire storage tank is produced in Kunststoffblasverfahren. The container wall comprises a plurality of material layers, of which at least one serves as a barrier layer. The wall of the storage tank is provided with a heat insulation, which at a certain point causes a greater insulation effect than other places, for example, in that the heat insulation only partially covers the wall of the container.

To reduce the pollutant NO _x in the exhaust gas of internal combustion engines, the SCR method (Selective Catalytic Reduction) has prevailed, in which the pollutant NO _x contained in the exhaust gas of the internal combustion engine with the aid of liquid reducing agent to N ₂ and H ₂ O is reduced. The reducing agent, which is urea or an aqueous urea solution, is usually transported by a pump, which represents the delivery module in a line from the storage tank to the metering module, where the reducing agent is introduced into the exhaust tract of an internal combustion engine. The pressure is controlled at the actuator via the speed of the pump motor and in the feedback branch via a pressure sensor. In current systems, a permanent Rückströmdrossel is also provided in the vicinity of the pressure generator, which gives the hydraulic system a fairly high control pressure stability.

To exclude any damage to the metering system for introducing the reducing agent into the exhaust gas of the internal combustion engine by freezing, the system is vented when switching off the internal combustion engine by reversing the feed pump with simultaneous opening of the metering to the exhaust gas. The risk of freezing is due to the fact that the reducing agent, which is usually urea or an aqueous urea solution, expands by about 10% by volume during freezing.

As a rule, storage tanks for receiving a reducing agent comprise a slosh pot in whose lower area a heating element is positioned. To ensure that a metering readiness can be achieved in an acceptable period of time with minimal heating power even at low temperatures, the heating element is limited to the bottom area of the slosh pot. By the plastic wall of the Schwapptopfes the content of the pot is isolated from the entire storage tank, so that the heating energy generated by the heating element for thawing the contents of Schwappopfes is available.

The design of the Schwapptopfes is usually chosen so that regardless of the prevailing liquid level in the storage tank Schwappopf is always completely filled. This offers at low temperatures in terms of range advantages, as thus a completely filled pot content is available for thawing by the heating element. As a rule, it is simultaneously extracted via two lines from the slosh pot and the storage tank. An appropriate throttle adjustment in both suction lines ensures that more than the dosing quantity is extracted from the tank. The return flow first flows into the slosh pot. This ensures that the slosh pot is always filled independently of the liquid level in the storage tank. The tank-side suction is due to the noise associated with the sloshing of the reducing agent in a closed cup, which has a hydraulic breakthrough to the tank volume of the storage tank in the upper area.

This design with two suction positions - in Schwappopf and in the storage tank - is associated with the disadvantage that the promotion of the reducing agent is exactly completed when the tank-side intake draws air, d. H. the storage tank is completely emptied. At this time, however, the Schwapptopf is still completely filled with reducing agent, an amount that can not be used by design, if it is sucked through two suction simultaneously from the slosh pot and the storage tank.

Overall, this represents a very unsatisfactory state.

Presentation of the invention

Following the solution proposed according to the invention, the delivery pump, ie the delivery module of the metering system, is again operated in the conveying direction for a short period of time after the venting process via the exhaust gas tract when the storage tank is virtually empty. This promotion, takes until the liquid column has reached the entrance of the delivery module, ie the delivery pump. Due to the backflow throttle opening of the valve is not required. By the repeated operation of the feed pump after the aeration process for a short period of time in the conveying direction are on a connection point of both suction lines, ie the opening into the tank suction line and the opening into the Schwapptopf suction line - both flooded.

If the delivery unit is switched off at this time, the delivery of the amount of reducing agent in the slosh pot via the suction line into the storage tank or into the lower bowl of the slosh pot takes place due to the effect of the hydrostatic pressure.

This Umpumpprozedur, ie the short operation of the delivery unit after the ventilation process in the conveying direction to build a liquid column can be performed at any time in principle, such. B. after parking the vehicle as well as during its operation. During the pumping process during operation, it must be ensured that sufficient NH _{3 has been} stored in the catalyst so that the NO _x emissions do not reach inadmissibly high values.

When the internal combustion engine is switched off, the volume exchange between the slosh pot and the lower pot of the supply tank will continue until the liquid levels in the slosh pot and in the lower pot have equalized.

For this reason, it is provided in a further advantageous embodiment of the invention underlying idea that Saucer has approximately half the volume of Schwappopfs. The hydraulic breakthrough in the lower pot to the volume of the stored in the storage tank reducing agent is arranged at a corresponding height. Furthermore, it has proved to be very advantageous if the suction point is as deep as possible in the Schwapptopf. For this purpose, the bottom of the Schwapptopfes can be partially formed in the direction of the tank bottom. A depression formed in the geometry of the floor then forms the space into which the suction line extending in the slosh pot or its suction point lies.

This measure ensures that the slosh pot does not run completely empty and thus the suction point at the slosh pot does not draw any air.

The steps outlined above for such. B. be carried out at an almost empty storage tank and after the ventilation process, d. H. the operation of the feed pump again briefly in the conveying direction after venting, assume that when parking the vehicle, the feed pump is reversed with simultaneous opening of the dosing. This ensures that the dosing system is ventilated and thus protected against the volume increase occurring when the reducing agent freezes.

By means of the sensor, which monitors the liquid level within the storage tank, it is determined that the liquid level in the storage tank is very low. The system will soon adjust the delivery of reducing agent, since air is sucked in at the tank-side suction point, since there is no longer any reducing agent. The Schwapptopf, which is formed within the storage tank, however, is completely filled.

A further advantage of the solution proposed according to the invention is that during the thawing process a cavity can form in the lower pot. This means that the suction point in the lower bowl sucks air, which would lead to an early dying of the system. In the pot, however, there is still enough liquid. By the procedure described above, the pot is refilled from the pot, so that the system could continue to operate.

Brief description of the drawings

In the appended drawings, the invention will be described in more detail below.

It shows:

1 the execution of a storage tank formed in the storage tank and Schwappopf suction points according to the prior art and

2 a variant of the proposed solution according to the invention.

1 shows a well-known from the prior art embodiment of a metering system with storage tank, Schwapptopf, delivery unit, pressure sensor, filter and dosing with a first suction line in the Schwapptopf and a second suction line into the tank.

1 is a dosing system 10 can be seen, which in particular for storing a reducing agent for introduction in the SCR process in the exhaust gas of an internal combustion engine, a storage tank 12 includes. In the storage tank is in particular a freezable reducing agent 13 , such as urea or a urea / water solution, added. The freezable reducing agent 13 freezes in the storage tank 12 depending on the addition of anti-freeze additives within a temperature range of -11 ° C to -40 ° C. The dosing system 10 includes next to the storage tank 12 , sump pot embedded in it 22 , a pumping unit 42 , a downstream pressure sensor 44 , a filter 46 and a dosing module 52 with which the liquid reducing agent 13 is injected into the exhaust tract of an internal combustion engine.

From the illustration according to 1 it can be seen that the storage tank 12 a floor 14 as well as a lid 16 having. Above the ground 14 of the dosing system 10 there is a saucer 18 which has a hydraulic breakthrough 20 with the volume of the storage tank 12 communicates.

From the illustration according to 1 shows that the hydraulic breakthrough 20 according to the embodiment known from the prior art at a height h ₁ above the tank bottom 14 or a sump formed in this.

Above the saucer 18 extends a Schwapptopf 22 , The sloshpot 22 is over a wall 24 limited, in which an overflow 26 is formed, in the illustration according to 1 at about the level of the liquid level 72 lies.

Above the bottom of the Schwapptopfes 22 is a heating element 28 arranged, which is usually operated electrically. The heating element 28 surrounds according to the in 1 represented representation of a first suction line 30 , The first suction line 30 flows at a suction point 34 in the saucer 18 , which relates to the geodesic height h ₁ relative to the sump in the storage tank 12 is arranged at a height h ₁ .

Furthermore, in the illustration according to 1 a second suction line 32 provided, which extends to near the bottom of Schwapptopfes 22 extends. The second suction line is by position 32 indicated and has a suction point 36 on, just above the bottom of Schwapptopfes 22 lies.

The first suction line 30 and the second suction line 32 extend to a junction 38 , which in the illustration according to 1 above the lid 16 of the storage tank 12 lies. Behind the association office 38 the first suction line 30 and the second suction line 32 extends a delivery line section 40 to the entrance of the pumping unit 42 , which is usually an electrically operated pump. On the output side is the delivery unit 42 a pressure sensor 44 downstream. Behind the pressure sensor 44 branches a return 48 off, with the excess reducing agent back into the storage tank 12 , especially in the Schwapptopf 22 , is traced back. In the return 48 there is a backflow throttle 50 , Downstream of the branch point of the return 48 is a filter 46 provided, to which the metering module 52 connects, via which the promoted reducing agent 13 is introduced into the exhaust tract of the internal combustion engine, so that the NO _x content of the gas is reduced by selective catalytic reduction in N ₂ and H ₂ O.

As shown in the illustration 1 it is ensured that the out of the return 48 escaping amount of reducing agent 13 not in the storage tank 12 but directly into the Schwapptopf 22 is encouraged. Thus, it is always guaranteed that the Schwapptopf 22 regardless of the liquid level 72 in the storage tank 12 is filled. The tank-side suction point 34 is due to the slosh movements of the reducing agent 13 occurring noise in the closed cup 18 , in the upper area the hydraulic breakthrough 20 , in a geodetic height h ₁ relative to the bottom of the sump of the storage tank 12 lies. This design with the extraction points with the suction points 34 respectively. 36 goes hand in hand with the disadvantage that the promotion of the reducing agent 13 then ended when at the suction point 34 in the lower pot 18 Air is drawn, ie the storage tank 12 is almost completely emptied. At this time, however, is the Schwapptopf 22 still complete with reducing agent 13 filled, a lot that by design in the 1 illustrated embodiment can no longer be used up because the delivery unit 42 while sucking in air at the suction point 34 no reducing agent promotes more and that in Schwappopf 22 stored reducing agent due to this connection to the ambient air no longer sucks.

In the illustration according to 2 is a variant of the present invention proposed solution of a dosing a storage tank, a Schwapptopf, a delivery unit, a pressure sensor, a filter and a metering module and two suction lines comprising, shown.

Unlike in 1 illustrated embodiment of a storage tank for a dosing system 10 for introducing a reducing agent 13 in the exhaust tract of an internal combustion engine, the second suction line extends 32 as deep as possible into a depression 38 a pot bottom 66 the Schwapptopfes 22 , The saucer 18 is modified so that its hydraulic breakthrough at a higher geodetic height h ₂ compared to the geodetic height h _{1 of} the hydraulic breakthrough 20 in accordance with the embodiment in 1 lies. With reference number 62 is that in the Schwapptopf 22 stored volume of the reducing agent 13 while in the lower pot 18 in accordance with the embodiment in 2 stored volume of the reducing agent 13 with reference number 64 is designated. The ratio of volumes 62 and 64 , which in Schwapptopf 22 or in the lower pot 18 be stored, is preferably at 2: 1. This means that inside the sloshpot 22 above the ground surface 66 the double Volume is stored compared to the volume in the lower pot 18 is stored.

From the illustration according to 2 also shows that above a lid 74 the Schwapptopfs 22 a bellows 70 finds, which is a continuation of the wall 24 represents the wall of the Schwapptopfs 22 represents and its volume in the storage tank 12 stored volume of the reducing agent 13 separates. reference numeral 72 marks the liquid level inside the storage tank 12 , Furthermore, the illustration according to 2 to see that the suction point 36 the second suction line 32 placed as low as possible in the slosh pot and at about the same geodetic height h with respect to the ground 14 of the storage tank 12 located as the suction point 34 the first suction line 30 that are in the saucer 18 extends.

With position 38 is the union point designated, at which the first suction line 30 in the saucer 18 runs and the second suction line 32 in the depression 68 the Schwapptopfs 22 dive in, unite. After the union office 38 extends the delivery line 40 to the suction side of a delivery unit 42 , which is preferably an electrically operated pump. This is analogous to the representation according to 1 the pressure sensor 44 downstream. Behind the pressure sensor 44 and in front of the filter 46 branches the return 48 over the excess reducing agent at too high pressure over the Rückströmdrossel 50 by means of the return 48 in the Schwapptopf 22 running back. Through the bellows 70 is ensured that the reducing agent 13 which is from the return 48 on the lid 16 of the storage tank 12 entering this, actually in the Schwapptopf 22 arrives. In contrast to the embodiment according to 2 is due to the depression 68 in the floor area 66 the Schwapptopfes 22 the second suction line 32 in an extension 76 formed at the bottom end, ie at a short distance above the bottom of the recess 68 the suction point 36 the Schwapptopfes 22 located.

The procedure provided according to the invention for the use of the volume of reducing agent contained in the sloshpot 13 at almost empty storage tank 12 will be described in more detail below. When parking the vehicle is the delivery unit 42 with simultaneous opening of the dosing module 52 , Dosing system 10 reversed. Because of that the delivery unit 42 Now operated in the opposite direction, the metering system 10 via the dosing module 52 ventilated and thus against the freezing of the reducing agent 13 Protected volume increase protected. By means of a in the illustration according to the 1 and 2 The liquid level sensor shown previously was found to be the liquid level 72 in the storage tank 12 is very low. In the solution according to the prior art - as in 1 shown - is the dosing system 10 soon stop the promotion, because at the suction 34 in the storage tank 10 only air is sucked in, whereas the Schwapptopf 22 inside the storage tank 12 is completely filled.

Following the procedure proposed according to the invention, a nearly empty storage tank is used 12 the delivery unit 42 After the ventilation process again briefly driven in the conveying direction. This delivery process, which is carried out after the aeration process, only lasts until the liquid column is the suction side of the delivery unit 42 has reached. because of in the return 48 provided Rückströmdrossel 50 is an opening of the dosing module 52 not mandatory. The Association Office 38 the two suction lines 30 respectively. 32 is thus flooded. This is a hydraulic connection between the slosh pot 22 and the saucer 18 at almost empty storage tank 12 about the two at the association office 38 shorted suction lines 30 respectively. 32 , Will at this time, ie in the flood of the Association 38 both suction lines 30 respectively. 32 the delivery unit 42 turned off, it is due to the hydrostatic pressure an overflow of the Schwapptopf 22 located volume 62 over the short-circuited suction lines 30 and 32 in the saucer 18 , This will be the saucer 18 in which there is an increased feed point 60 due to the nearly empty storage tank 12 no reducing agent 13 can flow over the serving in this case as a discharge suction point 34 the first suction line 30 again with reducing agent 13 filled so that at both suckling points 34 and 36 the two suction lines 30 respectively. 32 no air is drawn, but always into the reducing agent 13 - be it in the volume 62 be it in the volume 64 - immerse yourself.

This Umpumpvorgang, ie the internal overflow of the Schwapptopf 22 contained volume 62 inside the storage tank 10 in the saucer 18 can in principle be performed at any time, ie both after stopping the vehicle or during its operation, especially during the defrosting process, when at the extraction point 34 forms a cavity. When overflowing during operation of the motor vehicle is to ensure that sufficient NH _{3 is} stored in the catalyst, so that the NO _x emissions are not unduly large. When the internal combustion engine is turned off, the volume exchange between the volume 62 , which in Schwapptopf 22 is stocked and the volume 64 which is in the lower pot 18 is present, as long as take the liquid levels in the Schwapptopf 22 and the saucer 18 have approximated each other.

It is therefore, as shown in the illustration 2 shows, especially advantageous when the volume 64 which is in the lower pot 18 is stored, about half the volume of the Schwapptopf 22 stored volume 62 equivalent. 2 also shows that the increased feed point 60 is arranged at a geodetic height h ₂ , which is the height of the hydraulic breakthrough 20 in accordance with the embodiment in 1 , which is there designated h ₁ , significantly exceeds. The elevated feed point 60 is preferably formed funnel-shaped, so that the sloshing in the outer tank liquid can be passed into the lower pot.

From the illustration according to 2 it turns out that due to the in the floor area 66 the Schwapptopfs 22 trained depression 68 the two suction points 34 . 36 the two suction lines 30 . 32 are approximately at the same geodetic height h.

By training the depression 68 in the floor area 66 the Schwapptopfes 22 can be achieved in an advantageous manner that the suction point 36 the second suction line 32 in the sloshpot 22 as low as possible. This measure ensures that the Schwapptopf 22 not completely empty and thus at the Saugstelle 36 the suction line 32 in the sloshpot 22 the depression 68 opens, no air is sucked in and the system would stop its operation.

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 102006027487 A1 [0001]

Claims (14)

Process for promoting a reducing agent ( 13 ) from a storage tank ( 12 ) with a slosh pot ( 22 ) and a saucer ( 18 ) with the following process steps: a) detection of a low liquid level ( 72 ) in the storage tank ( 12 ), b) carrying out a polarity reversal of a delivery unit ( 42 ) when parking the vehicle and opening a dosing module ( 52 ) of a metering system, c) operation of the delivery unit ( 42 ) after process step b) briefly in the conveying direction until a junction ( 38 ) of suction lines ( 30 . 32 ) with reducing agent ( 13 ) is flooded and d) overflowing in Schwappopf ( 22 ) volume ( 62 ) due to the effect of the hydrostatic pressure over that at the junction ( 38 ) via the suction lines ( 30 . 32 ) in the storage tank ( 12 ) or the lower pot ( 18 ) from the Schwapptopf ( 22 ). Method according to claim 1, characterized in that the overflow of the reducing agent ( 13 ) in the storage tank ( 12 ) or the lower pot ( 18 ) until the liquid levels ( 72 ) in these correspond to each other. A method according to claim 1, characterized in that the promotion according to step c) is carried out until the liquid column in the suction lines ( 30 . 32 ), the Association Office ( 38 ) reached. A method according to claim 3, characterized in that by the polarity reversal of the delivery unit ( 42 ) and the operation of the delivery unit ( 42 ) against the conveying direction a ventilation of the dosing ( 10 ) he follows. A method according to claim 1, characterized in that the method steps c) and d) are carried out after the vehicle is parked and during the operation of the vehicle. Storage tank ( 12 ) of a dosing system ( 10 ) for storing an operating auxiliary for an internal combustion engine, in particular for receiving a reducing agent ( 13 ) with a slosh pot ( 22 ) and a saucer ( 18 ), for carrying out the method according to one or more of the preceding claims, characterized in that suction points ( 34 . 36 ) of suction lines ( 30 . 32 ) in volumes ( 62 . 64 ) of the Schwapptopfs ( 22 ) and the lower pot ( 18 protrude), wherein the suction points ( 36 . 34 ) are substantially at identical geodetic height h. Storage tank ( 12 ) according to claim 6, characterized in that the volumes ( 62 . 64 ) in the Schwapptopf ( 22 ) and in the lower pot ( 18 ) are hydraulically separated from each other. Storage tank ( 12 ) according to claim 6, characterized in that the ratio of the Schwapptopf ( 22 ) and in the lower pot ( 18 ) stored volumes ( 62 . 64 ) Is 2: 1. Storage tank ( 12 ) according to claim 7, characterized in that the volumes ( 62 . 64 ) of Schwapptopf ( 22 ) and saucer ( 18 ) through a floor surface ( 66 ) are hydraulically separated from each other. Storage tank ( 12 ) according to claim 6, characterized in that the bottom surface ( 66 ) a recess ( 68 ) into which the suction point ( 36 ) of the Schwapptopf ( 22 ) associated with suction line ( 32 ) protrudes. Storage tank ( 12 ) according to claim 6, characterized in that the suction lines ( 30 . 32 ) at a meeting point ( 38 ) open into each other before the suction side of a delivery unit ( 42 ) lies. Storage tank ( 12 ) according to one of claims 6 to 11, characterized in that a feed point ( 60 ) is formed on a raised geodesic level, in particular funnel-shaped, and the bottom pot ( 18 ) at a geodetic height h ₂ relative to the ground ( 14 ) of the storage tank ( 12 ), which determines the level of the soil ( 66 ) of the Schwapptopfes ( 22 ) exceeds. Storage tank ( 12 ) according to one of the preceding claims, characterized in that the suction point ( 36 ) of the second suction line ( 32 ), the Schwapptopf ( 22 ), in a depression ( 68 ) of the floor surface ( 66 ) of the Schwapptopfes ( 22 ) lies. Storage tank ( 12 ) according to one or more of the preceding claims, characterized in that the bottom surface ( 66 ) of the Schwapptopfes ( 22 ) one in the direction of the ground ( 14 ) of the storage tank ( 12 ) extending recess ( 68 ) having.

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