Reducing agent supply system for exhaust aftertreatment

Abstract

Reducing agent supply system (4) for an exhaust aftertreatment system (2) with: a reducing agent pump (14) which is configured to extract reducing agent from a reducing agent tank (10) and supply it to a Venturi nozzle (16) connected to an outlet of the reducing agent pump (14); a one-way valve (18) whose inlet is connected to an outlet of the Venturi nozzle (16); and a branch (16e) which leads into a narrow point (16c) of the Venturi nozzle (16); wherein the one-way valve (18) is designed to open at an opening pressure that is greater than the operating pressure of the exhaust aftertreatment system (2).

Description

[0001] The invention relates to a reducing agent supply system for exhaust gas aftertreatment. State of the art

[0002] Selective catalytic reduction (SCR) technology, using a urea-based reducing agent, has proven effective in reducing nitrogen oxides (NOx) from combustion engine exhaust gases, particularly diesel engines. Systems have been developed that ensure compliance with emissions limits by precisely adding an aqueous urea solution (AdBlue) as a reducing agent to the combustion engine's exhaust system and then reducing the nitrogen oxides in a subsequent SCR catalyst. These systems essentially comprise a urea solution tank, a delivery module with a filter and pump unit, a dosing module, and an electronic control unit.

[0003] To prevent damage from the pressure of freezing the reducing agent, the dosing module of such a system must be completely emptied when the system is switched off. This is usually achieved using a siphoning pump, which is activated after the engine is switched off to extract the reducing agent from the dosing module.

[0004] Document DE 10 2012 013 468 A1 discloses a reducing agent metering system for injecting a reducing agent into the exhaust gas stream of an internal combustion engine for selective catalytic reduction. The metering system is connectable to a reducing agent tank, from which the reducing agent is drawn and conveyed by a pump via a delivery line and introduced into the exhaust gas stream of the internal combustion engine through at least one nozzle. A Venturi tube is integrated into the delivery line, which has a branch that opens into the nozzle. An openable shut-off device is arranged at the outlet of the Venturi tube, so that when the shut-off device is open, the reducing agent contained in the nozzle and the branch is drawn into the Venturi tube as a suction medium and carried away via the outlet.

[0005] DE 10 2010 031 660 A1 discloses a method for operating a metering system, in particular for an SCR catalyst of an internal combustion engine, comprising a reducing agent tank, a conveying module, at least one metering module, and a pressure line. In the method, after completion of metering with the metering module closed and system pressure at all, at least one relief valve arranged between the reducing agent tank and the pressure line is first opened. Then the metering module is opened, allowing liquid reducing agent to be drawn back from the metering module into the pressure line. Disclosure of the invention

[0006] The object of the present invention is to provide a reducing agent supply system for an exhaust aftertreatment system that does not require an additional suction pump and is not damaged by freezing reducing agent at low temperatures.

[0007] According to one embodiment of the invention, a reducing agent supply system for an exhaust aftertreatment system comprises a reducing agent pump configured to draw reducing agent from a reducing agent tank and supply it to the inlet of a Venturi nozzle connected to an outlet of the reducing agent pump. The reducing agent supply system also comprises a one-way valve, the inlet of which is connected to an outlet of the Venturi nozzle, and a branch that opens into a constriction of the Venturi nozzle. The one-way valve is configured to open at an opening pressure that is greater than the operating pressure of the exhaust aftertreatment system.

[0008] The invention also includes an exhaust aftertreatment system with a reducing agent supply system according to the invention and with an injection device which is connected to the branch and is designed to inject reducing agent, which is supplied to the injection device through the branch, into an exhaust stream of an internal combustion engine.

[0009] The invention also includes a method for emptying an exhaust aftertreatment system with a reducing agent supply system according to the invention. The method comprises increasing the fluid pressure in the reducing agent supply system above the opening pressure of the one-way valve in order to open the one-way valve.

[0010] A reducing agent supply system according to exemplary embodiments of the invention makes it possible to almost completely empty the exhaust aftertreatment system, and in particular its injection device, without requiring an additional siphoning pump. This eliminates the cost and space required for a siphoning pump. Furthermore, the system design is simplified, and the system is less prone to maintenance and malfunctions. The effort associated with controlling a siphoning pump during operation is also eliminated.

[0011] In one embodiment, the one-way valve is designed to remain open at fluid pressures above a holding pressure that is lower than the opening pressure of the one-way valve. In this way, the exhaust aftertreatment system can be completely emptied, even if the fluid pressure in the exhaust aftertreatment system drops below the opening pressure after the one-way valve has opened.

[0012] In one embodiment, the opening pressure of the one-way valve is between 8 bar and 10 bar, particularly 9 bar. In another embodiment, the holding pressure of the one-way valve is between 0.25 bar and 0.75 bar, particularly 0.5 bar. These pressures have proven particularly suitable for operating and almost completely emptying the exhaust aftertreatment system.

[0013] In one embodiment, the one-way valve is designed as a diaphragm valve with an elastic diaphragm. A diaphragm valve is particularly suitable for achieving the desired opening and holding-open behavior of the one-way valve.

[0014] In one embodiment, the inlet of the one-way valve opens into a region opposite a central region of the elastic diaphragm of the diaphragm valve. In another embodiment, the outlet is located at a radial distance from the center of the diaphragm, the distance from the center of the diaphragm being greater than the radius of the central region of the diaphragm.

[0015] In this way, a one-way valve can be provided whose holding pressure is significantly lower than its opening pressure.

[0016] The central area of ​​the membrane can in particular have a diameter of 2 mm to 4 mm, in particular a diameter of 3 mm; and the outlet can have a distance of 8 mm to 9 mm, in particular a distance of 8.5 mm from the center of the membrane in order to achieve an opening pressure and a holding pressure in the respective desired area.

[0017] Exemplary embodiments of the invention are described below with reference to the drawings: Brief description of the drawings Fig. Figure 1 shows a schematic view of an exhaust aftertreatment system with a reducing agent supply system according to an embodiment of the invention. Fig. Figure 2 shows an enlarged view of a Venturi nozzle, as used in the [document / model]. Fig. The reducing agent supply system shown in section 1 is used. Fig. Figure 3 shows a cross-section through a one-way valve, as used in the Fig. The reducing agent supply system shown in section 1 is used. The Fig. Figures 4a to 4c show in schematic representation three operating states of an exhaust aftertreatment system according to an embodiment of the invention. Character description

[0018] Fig. Figure 1 shows a schematic view of an exhaust aftertreatment system 2 with a reducing agent supply system 4 according to an embodiment of the invention.

[0019] The reducing agent supply system 4 includes a tank 10 in which liquid reducing agent is stored.

[0020] A reducing agent pump 14 is designed to extract reducing agent from the reducing agent tank 10 via a reducing agent extraction line 12 during operation and to supply it to an inlet of a Venturi nozzle 16.

[0021] A reducing agent return line 20, which is connected via a one-way valve 18 to an outlet of the Venturi nozzle 16 opposite the inlet of the Venturi nozzle 16, makes it possible to return reducing agent exiting the outlet of the Venturi nozzle 16 back into the reducing agent tank 10.

[0022] The Venturi nozzle 16 has a branch 16e which is connected via a metering module supply line 22 to a metering module 6 arranged on an exhaust stream 8 of an internal combustion engine 7.

[0023] Fig. Figure 2 shows an enlarged view of the Venturi nozzle 16.

[0024] The Venturi nozzle 16 has an inlet area 16a, which is connected to the outlet of the (in the Fig. 2 (not shown) reducing agent pump 14 is connected and opens on its side facing away from the reducing agent pump 14 into a constriction region 16b, the cross-section of which is in the flow direction of the fluid (in the illustration of the Fig. 2 (from bottom to top) narrows.

[0025] The minimum cross-section is reached at the narrowest point (constriction) 16c of the Venturi nozzle 16. Downstream behind (in the illustration of the Fig. 2 above the constriction 16c, there is a widening area 16d, the cross-section of which widens in the direction of fluid flow. The outlet of the widening area 16d is connected to the one in the Fig. 1 shown one-way valve 18 connected.

[0026] A branch 16e, which, as in the Fig. 1 shown, which is connected to the dosing module 6 by a dosing module supply line 22, leads into the constriction 16c of the Venturi nozzle 16.

[0027] Fig. Figure 3 shows a cross-section through a one-way valve 18 according to an embodiment of the invention.

[0028] The one-way valve 18 comprises two housing elements 24, 25 arranged coaxially along an axis A, between which an elastic diaphragm 26 is arranged, in particular clamped. The housing elements 24, 25 and the elastic diaphragm 26 are essentially rotationally symmetrical about the axis A.

[0029] At the center of a first, in the Fig. In the housing element 24 shown below, an inlet 34 is formed along axis A, which is connected to the outlet of the Venturi nozzle 16 during operation, as shown in the Fig. 1 shown.

[0030] When the one-way valve 18 is closed, the diaphragm 26 rests at a radial distance R1 from the axis A on a surface of the first housing element 24 facing the diaphragm 26, so that the inlet 34 is sealed fluid-tight by a central area 27 of the diaphragm 26.

[0031] At a radially larger distance R2 > R1 from axis A, a drain 36 is formed, which is connected to the one in the Fig. 3 not shown return line 20 is connected (see Fig. 1) When the one-way valve 18 is open, the fluid is discharged from the one-way valve 18 through the outlet 36.

[0032] On the side facing away from the first housing element 24 (in the Fig. On the side of the membrane 26 shown above (3), a plunger 28 is arranged in the central area 27 of the membrane, which is made of plastic, for example.

[0033] Between the plunger 28 and a spring support cover 30, which is arranged within the second housing element 25, there is an elastic element 32, for example a compression spring. The elastic element 32 presses the plunger 28 and thus also the central area 27 of the diaphragm 26 against the surface of the first housing element 24 facing the diaphragm 26, in order to close the one-way valve 18 fluid-tight.

[0034] If the fluid pressure in the inlet 34 exceeds a predetermined limit value (“opening pressure”) of, for example, 9 bar, the central area 27 of the diaphragm 26 is pressed by the fluid against the force of the elastic element 32, so that an opening is formed between the diaphragm 26 and the surface of the first housing element 24, which faces the diaphragm 26, through which the fluid can flow from the inlet 34 into the outlet 36.

[0035] In the event of a subsequent pressure drop in the inlet 34, the diaphragm 26 remains in an open state even at fluid pressures below the specified opening pressure, for example, at fluid pressures above 0.5 bar. In other words, an initial, higher fluid pressure ("opening pressure") is necessary to open the one-way valve 18. A second fluid pressure ("holding pressure"), which is lower than the opening pressure, is sufficient to keep the open one-way valve 18 in its open state.

[0036] In the Fig. Figures 4a to 4c schematically show three operating states of an exhaust aftertreatment system 2 according to an embodiment of the invention.

[0037] Fig. Figure 4a illustrates the dosing operation in which reducing agent is injected from the reducing agent tank 10 into the exhaust stream 8.

[0038] In this operating state, the reducing agent pump 14 delivers reducing agent from the reducing agent tank 10 and thereby generates a fluid pressure at the one-way valve 18 that is below the opening pressure of the one-way valve 18. The one-way valve 18 is therefore closed, and the reducing agent delivered by the reducing agent pump 14 flows from the connection 16e of the Venturi nozzle 16 through the metering module supply line 22 to the metering module 6, which is in operation and injects the reducing agent into the exhaust gas stream 8 in the desired quantity.

[0039] In order to empty the exhaust aftertreatment system 2 and in particular the metering module 6 after the combustion engine 7 has been switched off, i.e. to remove the reducing agent from the metering module 6, the exhaust aftertreatment system 2 is put into a second operating state, which is in the Fig. 4b is shown.

[0040] In this second operating state, the dosing module 6 is deactivated and closed. The fluid pressure in the inlet 34 of the one-way valve 18 is increased by appropriately controlling the reducing agent pump 14 until the predetermined opening pressure of the one-way valve 18 is exceeded.

[0041] When the specified opening pressure is exceeded, the one-way valve 18 opens, and the fluid pumped by the reducing agent pump 14 flows through the Venturi nozzle 16, the open one-way valve 18 and the return line 20 back into the tank 10.

[0042] After the one-way valve 18 is opened, the exhaust aftertreatment system 2 is brought into a third operating state, which is in the Fig. 4c is shown.

[0043] Starting from the second operating state, as described in the Fig. As shown in 4b, the dosing module 6 is opened so that it is in fluid contact with the branch 16e of the Venturi nozzle 16 via the dosing module supply line 22.

[0044] Due to the previously described flow of the reducing agent through the Venturi nozzle (see Fig. 4b) and the resulting narrowing at point 16c (see Fig. 2) Due to the Bernoulli effect resulting from the Venturi nozzle 16, the reducing agent is drawn from the dosing module 6 and the dosing module supply line 22 by the Venturi nozzle 16 and is returned to the fluid tank 10 through the open one-way valve 18 and the return line 20.

[0045] In this operating state, the fluid pressure at the one-way valve 18 is lower than the opening pressure of the one-way valve 18 but higher than the holding pressure of the one-way valve 18, so that the one-way valve 18 remains open. The fluid pressure at the one-way valve 18 in this operating state can, for example, be in the range between 0.5 bar and 9 bar.

[0046] After the dosing module 6 and the dosing module supply line 22 have been completely emptied in the manner described, the reducing agent pump 14 is switched off. As a result, the fluid pressure at the one-way valve 18 falls below the holding pressure, so that the one-way valve 18 closes and the exhaust aftertreatment system 2 is returned to its initial operating state by activating the reducing agent pump 14. Fig. 4a can be operated.

[0047] A reducing agent supply system 4 according to an embodiment of the invention makes it possible to empty the metering module 6 of an exhaust aftertreatment system 2 in order to prevent damage from freezing reducing agent, without the need for an additional return pump. The effort and costs for manufacturing the exhaust aftertreatment system 2 can thus be significantly reduced.

Claims

[1] Reducing agent supply system (4) for an exhaust aftertreatment system (2) comprising: a reducing agent pump (14) which is configured to extract reducing agent from a reducing agent tank (10) and supply it to a Venturi nozzle (16) connected to an outlet of the reducing agent pump (14); a one-way valve (18) whose inlet is connected to an outlet of the Venturi nozzle (16); and a branch (16e) which leads into a narrow point (16c) of the Venturi nozzle (16); wherein the one-way valve (18) is designed to open at an opening pressure that is greater than the operating pressure of the exhaust aftertreatment system (2). [2] Reducing agent supply system (4) according to claim 1, wherein the one-way valve (18) is configured to remain open at fluid pressures above a holding pressure which is less than the opening pressure of the one-way valve (18). [3] Reducing agent supply system (4) according to claim 2, wherein the holding pressure is between 0.25 bar and 0.75 bar, in particular 0.5 bar, and / or wherein the opening pressure is between 8 bar and 10 bar, in particular 9 bar. [4] Reducing agent supply system (4) according to one of the preceding claims wherein the one-way valve (18) has a membrane (26). [5] Reducing agent supply system (4) according to claim 4, wherein the inlet (34) of the one-way valve opens into a central area (27) of the membrane (26). [6] Reducing agent supply system (4) according to claim 5, wherein the central area (27) of the membrane (26) has a radius (R1) between 1 mm and 3 mm, in particular a radius (R1) of 1.5 mm. [7] Reducing agent supply system (4) according to any one of claims 4 to 6, wherein the outlet (36) is arranged at a distance (R2) from the center (Z) of the membrane (26) which is greater than the radius (R1) of the central region (27) of the membrane (26). [8] Reducing agent supply system (4) according to claim 7, wherein the distance (R2) of the outlet (36) from the center (Z) of the membrane (26) is between 8 mm and 9 mm, in particular 8.5 mm. [9] Exhaust aftertreatment system (2) with a reducing agent supply system (4) according to any of the preceding claims and an injection device which is connected to the branch (16e) and is designed to inject reducing agent into an exhaust stream (8) of an internal combustion engine (7). [10] Method for emptying an exhaust aftertreatment system (2) according to claim 9, wherein the method comprises increasing the fluid pressure in the exhaust aftertreatment system (2) above the opening pressure of the one-way valve (18) in order to open the one-way valve (18).

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