WO2009153085A1

WO2009153085A1 - Dosing system for a liquid medium, particularly a urea-water solution

Info

Publication number: WO2009153085A1
Application number: PCT/EP2009/054799
Authority: WO
Inventors: Guenther Vogt; Stefan Loesch; Christian Basan
Original assignee: Robert Bosch Gmbh
Priority date: 2008-06-17
Filing date: 2009-04-22
Publication date: 2009-12-23
Also published as: CN102066709A; US20110186153A1; ATE546622T1; EP2294294B1; EP2294294A1; DE102008002467A1

Abstract

The invention relates to a dosing system for a liquid reduction medium enabling precise dosing of the reduction medium in the exhaust gas system of an internal combustion engine. This is carried out particularly by means of a quick and safe closing of a pressure-actuated dosing valve (13). Simultaneously, the dosing system according to the invention also enables the dissipation of the pressure impulses resulting due to the closing movement of the dosing valve (13).

Description

description

title

Dosing system for a liquid medium, in particular urea-water solution.

State of the art

The emission limit values for nitrogen oxides in motor vehicles whose weight exceeds a certain limit require exhaust aftertreatment devices which carry out a selective catalytic reduction (SCR) of the nitrogen oxides contained in the raw emissions of the internal combustion engine. This so-called SCR process for exhaust gas purification is known from the prior art, so that it is possible to dispense with a detailed explanation of the chemical processes taking place in this process.

An example of such an exhaust aftertreatment device is known from DE 10 2006 012 855 Al. There, an aqueous urea solution is stored in a tank and injected by a metering pump and with the aid of a metering valve as needed in an exhaust pipe of the internal combustion engine. The known from DE 10 2006 012 855 Al metering valve is pressure-actuated. This means that it opens as soon as a predetermined opening pressure is exceeded at the inlet of the metering valve. As soon as the opening pressure is fallen below, the dosing valve closes again.

The pressure-actuated dosing valve is a "passive" component that does not require its own control, nor are signal lines or control lines from a control unit to the dosing valve required.

Disclosure of the invention

The invention has for its object to further develop a metering system of the type mentioned in that the use characteristics, in particular the Precision is injected with the reducing agent in the exhaust pipe, is improved. In addition, tightness of the metering valve should be increased during operation and after switching off the internal combustion engine.

This object is achieved in a metering system for a liquid medium, in particular a liquid reducing agent, such as an aqueous urea-water solution, with a tank, with a metering pump and with a metering valve, wherein a pressure side of the diaphragm pump and the metering valve by a first line are connected to each other and wherein the tank and a suction side of the metering pump are connected to each other by a second line, achieved in that in the first line, a first check valve is provided.

The first check valve prevents the first line from draining between two actuations of the metering valve. This would mean that during the subsequent actuation of the metering pump, the quantity of urea-water solution predefined by an engine control unit is not injected. As a result, the quality of the exhaust aftertreatment would suffer and emissions would rise.

In a further advantageous embodiment of the invention it is provided that a lifting movement of the metering pump is at least partially transmitted to the valve member of the first check valve.

This means that, starting from an idle state of the metering pump, the metering pump initially executes a delivery stroke and conveys the liquid reducing agent into the first conduit. In a delivery stroke, the valve member of the first check valve opens when the pressure in the metering pump is greater than the opening pressure of the first check valve, and the promotion of reducing agent to the metering valve begins.

By the inventive transmission of the lifting movement of the metering pump on the valve member is namely ensured that the first check valve during the

Suction stroke remains open regardless of the pressure conditions. As a result, a predetermined amount of urea water solution from the first line is sucked back into the metering pump, so that a controlled and rapid pressure reduction takes place in the first line and in the metering valve. As a result, the metering valve closes quickly and tightly, so that the dosage of the reducing agent is carried out with higher accuracy.

Just before the metering pump has reached its starting point and the stroke of the metering pump is equal to zero, the lifting movements of the metering pump and the valve member are decoupled, so that the first check valve can fulfill its function known from the prior art and hydraulically separates the first line from the metering pump , Finally, the venting of the metering system is facilitated by the coupling of valve member and stroke of the metering pump. If a compressible medium, such as air or steam, is located in a delivery chamber of the metering pump, it can be ensured by the forced opening of the first check valve that the air or the vapor in the delivery chamber of the metering pump is pushed out into the first conduit and thereby a venting of the metering takes place. As soon as only liquid reducing agent is present in the metering pump, this promotes full again and pushes the existing in the suction line vapor bubbles or air bubbles over time through the metering valve from the metering system. In order to achieve a safe closing and a better operating behavior, it is further provided that the first check valve is spring-loaded.

In a further advantageous embodiment of the invention is further provided that the first check valve is designed as a double-acting check valve, and that a second output of the first check valve is hydraulically connected to the tank via a connecting line. This prevents unintentional and reopening of the metering valve after switching off the metering pump.

In the promotion of liquid reducing agent through the metering pump opens the first check valve and the reducing agent passes from the metering pump in the first line. After the delivery and injection of the reducing agent through the metering valve in the exhaust system, the first check valve closes again. The closing of the metering valve creates a pressure surge in the first line, which is reflected by a single-acting check valve and runs again to the metering valve. There, the pressure surge can trigger a brief opening of the metering valve. As a result, a non-negligible amount of the reducing agent is undesirably injected into the exhaust pipe. This effect increases with increasing closing speed of the metering valve.

If now the first check valve is designed as a double-acting check valve, then closes the check valve during the promotion of the metering pump, a connecting line between the first line and the tank of the dosing. In this position, the metering system behaves, not unlike a metering system according to the invention with a simply designed check valve.

But when the delivery stroke of the metering pump is completed, the valve member of the double-acting check valve is pushed back into the valve seat and the hydraulic connection between the metering pump and metering valve is interrupted. At the same time a hydraulic connection between the first line is made to the non-pressurized tank via the connecting line, so that an outgoing from the metering pressure surge is not reflected at the first check valve, but runs into the tank and is dissipated there. As a result, the above-described unwanted Nachspritzer be avoided due to pressure surges within the metering.

In a further advantageous embodiment of the invention, it is provided that in the connecting line, a pressure-holding valve, in particular an adjustable pressure-holding valve, is provided. The opening pressure of the pressure holding valve is chosen to be lower than the opening pressure of the metering valve, since only then can the reflection of pressure surges be reliably prevented. Due to the holding pressure of the pressure holding valve, it is possible to suppress the formation of vapor bubbles within the first conduit or of the metering system and thereby further improve the function and accuracy with which the reducing agent is injected and metered.

Further advantages and advantageous embodiments of the invention are the following drawings, the description and the claims removable. All of the features disclosed in the drawing, the description and the claims can be essential to the invention both individually and in any combination with one another.

Show it:

Figure 1 shows the schematic structure of a metering system according to the invention and Figures 2, 3 embodiments of metering systems according to the invention.

In Figure 1, an internal combustion engine 1 with an exhaust gas aftertreatment device 3 is greatly simplified and shown schematically. The exhaust aftertreatment device 3 comprises an exhaust pipe 5, an oxidation catalyst 7 and a S C R catalyst 11. The flow direction of the exhaust gas through the exhaust pipe 5 is indicated by arrows (without

Reference numeral). In order to supply the SCR catalytic converter 11 with reducing agent, a metering valve 13 for the reducing agent is arranged upstream of the SC R catalytic converter 11 on the exhaust gas pipe 5. The metering valve 13 injects reducing agent upstream of the SCR catalyst 11 into the exhaust pipe 5 as needed. The metering system according to the invention comprises the metering valve 13, a metering pump 15 and a storage tank 17. The metering pump 15 is shown only as a "black box" in Figure 1. Details of this are explained below with reference to Figures 2 and 3. Between the metering pump 15 and the metering valve 13, a first line 19 is provided. Between the tank 17 and the metering pump 15, a second conduit 21 is provided.

For the sake of completeness, reference should still be made to the sensors arranged in the exhaust system, namely an NOX sensor 25 and temperature sensors 23 and 27. These sensors 23, 25 and 27 are connected via signal lines (without reference numeral) to a control unit 29 of the internal combustion engine. This control unit 29 controls the internal combustion engine 1 and, inter alia, the metering pump 15. The line connection between the control unit 29 and the metering pump 15 is shown by a dashed arrow (without reference numerals) in Figure 1.

A first embodiment of a metering system according to the invention is shown and explained with reference to FIG. The same components are provided with the same reference numerals and as with respect to the Figure 1 said accordingly. The metering valve 13 is shown schematically as a spring-loaded valve. The metering pump 15 is designed as a diaphragm pump with a membrane 31. The

Diaphragm 31 of metering pump 15 is actuated by an electromagnet comprising a coil 33 and an armature 35. When the coil 33 is energized, the armature 35 and with it the diaphragm 31 moves upward in FIG. 2 and performs a delivery stroke. The stroke H is shown in FIG. The rest position shown in Figure 2 of the diaphragm 31 and the armature 35 corresponds to a stroke H = O.

Between a delivery chamber 37 of the metering pump 15 and the first line 19, a first check valve 39 is arranged. The first check valve 39 is shown in FIG. 2 as a flutter valve comprising a valve member 41 and a valve seat 43. In these flutter valves, the valve member 41 is formed as an elastic membrane of a plastic, such as EPDM, or metal. A spring 44 exerts a force in the closing direction of the first check valve 39 on the valve member 41.

The lifting movement of the diaphragm 31 is partially transmitted to the valve member 41 via a plunger 45. This happens because in the rest position of the membrane 31 and when the first check valve 39 is closed, the plunger 45 does not rest on the membrane 31.

Between the diaphragm 31 facing the end of the plunger 45 and the diaphragm 31 in this state, a distance H _MIN - As soon as the stroke H is greater than H _MIN , the diaphragm lifts the valve member 41 from the valve seat 43 by means of the plunger 45. This coupling of the valve member 41 with the stroke H of the diaphragm 31 of the metering pump causes the first check valve 39, regardless of the pressure conditions in the first conduit 19 and in the delivery chamber 37 during the intake stroke remains open long. Consequently is sucked back into the delivery chamber 37 by the suction movement of the diaphragm 31, a portion of the reductant located in the first conduit 19. As a result, a pressure reduction takes place in the line 19 and the metering valve 13 closes quickly and tightly.

Between the delivery chamber 37 and the second line 21, a second check valve 46 is arranged, which prevents 15 reducing agent from the delivery chamber 37 in the second conduit 21 and the tank 17 can flow back during the delivery stroke of the metering pump. This second check valve 46 is not spring-loaded as a rule. It is also often formed as a flutter valve, although it is shown symbolically in Figure 2 and 3 as a ball valve. FIG. 3 shows a further exemplary embodiment of a metering system according to the invention. In this embodiment, the first check valve 39 is formed as a double-acting check valve and shown symbolically as a ball valve, although it is also usually a flutter or sniffer valve. The first check valve 39 has not only the first valve seat 43, but also a second valve seat 47, the output of which is hydraulically connected to the tank 17 via a connecting line 49 and the second line 21. As soon as the metering pump 15 starts to deliver reducing agent, the pressure in the delivery chamber 37 rises above the pressure prevailing in the first line 19. As a result, the valve member 41 lifts off from the first valve seat 43 and closes the connection line 49 because it is sealingly pressed onto the second valve seat 47. At the same time thereby the hydraulic connection between the delivery chamber 37 and the first line 19 is released and the promotion of reducing agent in the first line 19 begins. The delivery stroke runs in the same way from the second exemplary embodiment, as explained with reference to the first exemplary embodiment according to FIG. Now, when the promotion has ended and the membrane 31 returns to its original position, the pressure conditions in the first check valve 39 ensure that the valve member 41 is pressed against the first valve seat 43 and thereby interrupted the hydraulic connection between the pumping chamber 37 and the first line 19 becomes. At the same time, a hydraulic connection between the first line 19, connecting line 49, second line 21 and tank 17 is opened, so that possibly run out of the metering valve 13 pressure surges run into the tank 17 and are dissipated there.

Optionally, a pressure-maintaining valve 51 is provided in the connecting line 49. The pressure holding valve 51 serves to maintain a minimum settable pressure in the first conduit 19 so that the boiling point of the reducing agent in the first conduit 19 is increased and the formation of vapor bubbles is suppressed. Advantageously, the

Opening pressure of the pressure holding valve 49 lower than the opening pressure of the metering valve 13, so that the closing movement and the sealing of the metering valve 13 are not prevented by the pressure-holding valve 51. In addition, this pressure surges whose amplitude is higher than the opening pressure of the pressure holding valve 51 continue to flow almost unhindered in the tank 17 and are dissipated there. In a particularly advantageous embodiment of the invention, the pressure holding valve 51 is adjustable with respect to its holding pressure, so that it can be adjusted according to the prevailing operating conditions. This makes it possible, for example, after stopping the engine to change the holding pressure, so that the first line 19 is completely depressurized and thus the metering valve 13 is completely sealed even over a longer period. If the risk of vapor bubble formation occurs during the operation of the internal combustion engine, the holding pressure of the pressure holding valve 51 can be increased accordingly.

FIG. 3b shows a block diagram of the exemplary embodiment according to FIG. 3a. In addition, various pressure sensors 53.1, 53.2 and 53.3 are shown, which are installed as required and connected to the control unit 29.

Claims

claims

1. dosing system for a liquid medium, in particular a liquid reducing agent, such as an aqueous urea-water solution (HWL), with a tank (17), with a metering pump (15) and with a metering valve (13), wherein a Pressure side of the metering pump (15) and the metering valve (13) by a first line (19) are interconnected and wherein the tank (17) and a

Suction side of the metering pump (15) by a second line (21) are interconnected, characterized in that in the first conduit (19) a first check valve (39) is provided.

2. dosing system according to claim 1, characterized in that a lifting movement of the metering pump (15) at least partially on the valve member (41) of the first

Check valve (39) is transmitted.

3. Dosing system according to claim 2, characterized in that the metering pump comprises a diaphragm (31), and that the lifting movement (H) of the diaphragm (31) is at least partially transmitted to the valve member (41) of the first check valve (39).

4. Dosing system according to claim 3, characterized in that the valve member (41) of the first check valve (39) is lifted from a first valve seat (43) as soon as the stroke movement of the metering pump (15) exceeds a minimum _stroke (H _mιn ).

5. Dosing system according to one of the preceding claims, characterized in that the first check valve (39) is spring-loaded.

6. Dosing system according to one of the preceding claims, characterized in that the first check valve (39) is designed as a double-acting check valve, and that a second valve seat (47) of the first check valve (39) with the tank (17) or the suction side of the metering pump (15) via a connecting line (49) is hydraulically in communication.

7. Dosing system according to claim 5, characterized in that in the connecting line (49), a pressure-holding valve, in particular an adjustable pressure-maintaining valve (51), is provided.

8. Dosing system according to one of the preceding claims, characterized in that in the second line (21) a second check valve (46) is provided.

9. dosing system according to one of the preceding claims, characterized in that the metering valve (13) is pressure-actuated.

10. Dosing system according to one of the preceding claims, characterized in that the diaphragm pump (15) by an actuator of an actuator, in particular an armature (35) of an electromagnet (33) is actuated.