KR20210044155A - Method for operating a feeding and dosing system for the reducing agent solution of at least one scr-catalytic converter - Google Patents

Abstract

The present invention relates to a method for operating a conveying and metering system for a reducing agent solution in one or more SCR catalytic converters of an internal combustion engine, wherein the conveying and metering system includes one or more conveying pumps; one or more re-suction pumps; one hydraulic supply line; and a plurality of metering supply valves connected to the hydraulic supply line. After the stop of the internal combustion engine, re-suction (82) of a reducing agent is carried out from at least the parts of the conveying and metering system while the metering supply valves are closed. Next, all metering feed valves are opened simultaneously (84).

Description

METHOD FOR OPERATING A FEEDING AND DOSING SYSTEM FOR THE REDUCING AGENT SOLUTION OF AT LEAST ONE SCR-CATALYTIC CONVERTER}

The present invention relates to a method of operating a conveying and metering system for a reducing agent solution of one or more SCR catalytic converters of an internal combustion engine. Further, the present invention relates to a computer program for executing each step of the method, and to a machine-readable storage medium storing the computer program. Finally, the present invention relates to an electronic control device configured to perform the method.

In order to reduce the proportion of nitrogen oxides in the exhaust gas of an internal combustion engine, in particular a diesel engine, it is known to arrange an SCR catalytic converter (Selective Catalytic Reduction) in the exhaust gas line of an internal combustion engine. The SCR catalytic converter reduces nitrogen oxides contained in exhaust gas to nitrogen in the presence of ammonia as a reducing agent. To provide ammonia, a reducing agent solution is metered into the exhaust gas line upstream of the SCR catalytic converter. Usually, for this purpose, an aqueous solution of urea containing urea (Urea Water Solution: UWS) is used as an ammonia separation reagent. 32.5% of UWS is on the market under the name ^{"AdBlue ® ".} This aqueous solution of urea is frozen at a temperature of -11.5°C.

In order to protect the metering supply valve and pressure line from damage from ice pressure during freezing, the SCR metering systems are evacuated or ventilated through resuction when the internal combustion engine is stopped. In metering mode, the system is pressurized through operation of a transfer pump. After the stoppage of the internal combustion engine, the release of the system pressure is effected by stopping the transfer pump and, in some cases, by opening the pressure reducing valve or the recirculation pump. When the metering supply valve is shut off, negative pressure is created in the system through vacuum by the recirculation pump. Thereafter, the metering supply valve is opened upon continuous evacuation of the system. For this reason, rapid air intake at the metering supply valve is executed. The vacuuming process continues until the negative pressure in the system stabilizes.

A metering system for liquid reducing agents that can be evacuated by means of a recirculation pump is described in DE 10 2011 081 628 A1.

The method is used for operation of a conveying and metering system for a reducing agent solution of one or more SCR catalytic converters of an internal combustion engine, wherein the conveying and metering system comprises at least one transfer pump; One or more resuction pumps; One hydraulic supply line; And a plurality of, in particular, two metering supply valves connected to the hydraulic supply line. In this case, the transfer pump and the recirculation pump can also be implemented with only one pump that can be operated in different transfer directions. A metering system of this type can be provided, for example, for an SCR catalytic converter system with two SCR catalytic converters, the first metering supply valve being arranged upstream of the first SCR catalytic converter in the exhaust gas line, and The two metering system is arranged between the SCR catalytic converters.

After the shutdown of the internal combustion engine, while the metering supply valves are shut off, at least the conveying and resuction of the reducing agent from the parts of the metering system is carried out. Then, all metering supply valves are opened simultaneously.

Through the formation of negative pressure prior to opening of the metering supply valves, the unintended metering supply of a small amount of reducing agent solution during the resuction process can be prevented. Metering supply valves open only when negative pressure is applied to them. In addition, the vacuuming process of the metering supply valves is carried out very rapidly in this way. This evacuation occurs dynamically better than when recirculation is initiated with the metering supply valves already open, since less reducing agent solution remains in the metering supply valve. By opening all the metering supply valves at the same time, the vacuuming process of the other metering supply valves is prevented from being delayed, as release of the negative pressure has already occurred due to the premature opening of one metering supply valve.

Preferably, the metering supply valves are only open when the negative pressure in the delivery and metering system is at least 5000 pascals. Particularly preferably, the metering supply valves are only opened when the negative pressure is at least 15000 Pascals. This ensures that the evacuation process of the metering supply valves is carried out so rapidly that the reducing agent solution cannot unintentionally reach the exhaust gas line. In this case, the negative pressure does not mean the absolute value of the pressure, but means a relative negative pressure with respect to the ambient pressure.

If there is no pressure sensor for measuring the pressure in the hydraulic supply line, it is instead preferred that the metering supply valves are opened after a predetermined period. Preferably, this period ranges from 5 seconds to 10 seconds.

Preferably, re-suction of the reducing agent is resumed after the metering supply valves are opened. Due to this, an additional reducing agent solution volume can be extracted from the sections of the hydraulic supply line which are led to the metering supply valves. This leads to an improvement in the robustness of the movement of the reducing agent solution in the hydraulic supply line, which may cause ice pressure at low temperatures.

Preferably, the resuction upon opening of the metering supply valves is carried out, at most, for a predetermined period of time. Due to this, too much air is prevented from entering the hydraulic supply line. The predetermined period of time is preferably at most 2 seconds, particularly preferably at most 1 second.

The computer program of the present application is specifically configured to execute each step of the method of the present application when executed on a computing device or an electronic control device. This allows different embodiments of the present method to be implemented in an electronic control device without the need to carry out structural changes. To this end, the computer program is stored in a machine-readable storage medium.

By installing the computer program in a conventional electronic control device, an electronic control device configured to operate a conveying and metering system for a reducing agent solution of one or more SCR catalytic converters is obtained by the method of the present disclosure.

Embodiments of the present invention are shown in the drawings and are described in more detail in the detailed description below.
1 is a schematic diagram of the components of a conveying and metering system for a reducing agent solution of an SCR catalytic converter that can be operated by an embodiment of the method according to the invention.
2 is a flow diagram of an embodiment of a method according to the invention.

1 schematically shows the components of a conveying and metering system with a conveying pump 10, a hydraulic supply line (pressure line) 20, and two metering supply valves 31, 32. A suction valve 11 and a pressure valve 12 are assigned to the transfer pump 10, and a throttle 13 is positioned upstream of the pressure valve 12. A filter 14 is located upstream of the intake valve 11. In the region of the supply line 20, a pressure sensor 21 and a pulsation damper 22 for measuring the pressure p are located. By the transfer pump 10, the liquid reducing agent solution is extracted from the supply unit (tank) 60 through the filter 61, and through the T-shaped branch in the hydraulic supply line 20, two metering supply valves 31 , 32), and metered on demand into an exhaust gas line not shown in the figure seen there. An additional filter 48 in a separate resuction path 41 of the system for resuctioning the icingable reducing agent solution from the ice pressure sensitive metering supply valves 31 and 32 and optionally from the supply line 20. A resuction pump unit 40 is provided which is arranged with ). The resuction pump unit 40 includes a unique resuction pump 42 to which an intake valve 43 and a pressure valve 44 are assigned. Parallel to the pressure valve 44, a bypass line 45 with a throttle 46 is located. One ice pressure damper 15 and 47 is located, respectively, within the range of the suction area of the transfer pump 10 and downstream of the resuction pump 42 in the return path of the system. The various elements of the conveying and metering system are integrated within the conveying module 50, which also includes a resuction pump unit 40.

After the shutdown of the internal combustion engine, the reducing agent solution passes through the resuction path 41 from the metering supply valves 31 and 32 and, in some cases, also partially or completely from the supply line 20 by means of the resuction pump 42. It is transferred back into the tank 60 through. The control of the transfer pump 10, the recirculation pump 42 and the metering supply valves 31, 32 is executed through the electronic control device 70.

2 shows the process of the method in the first embodiment of the present invention. After the start of the method 80, a first check 81 is carried out as to whether the internal combustion engine has been stopped. When the switch-off is executed, the transfer pump 10 is switched off, the resuction pump 42 is first opened, and then switched on to start the re-suction 82 of the reducing agent solution. In this case, the metering supply valves 31 and 32 are shut off. As soon as the second inspection 83 shows that the negative pressure p measured by the pressure sensor 21 has thereby dropped below 1500 Pascals, the simultaneous opening 84 of the two metering supply valves 31 and 32 Is executed. After these metering supply valves are shut off again, resuction is resumed for 1 second, at which time the metering supply valves 31 and 32 are simultaneously or Open continuously. Thereafter, the recirculation pump is switched off (85), and the method ends (86).

The second embodiment of the present invention differs from the first embodiment in that whether or not the negative pressure p measured by the pressure sensor 21 has dropped below 1500 Pascals is not inspected in the second inspection 83. Instead, it is checked whether a period of 7 seconds has elapsed since the recirculation pump 42 is switched on.

Claims (10)

A method of operating a conveying and metering system for a reducing agent solution of at least one SCR catalytic converter of an internal combustion engine, wherein the conveying and metering system comprises at least one transfer pump 10; One or more resuction pumps 42; One hydraulic supply line 20; And a plurality of metering supply valves (31, 32) connected to the hydraulic supply line (20), comprising:
After the shutdown of the internal combustion engine, while the metering supply valves 31, 32 are shut off, at least a resuction 82 of the reducing agent from the parts of the conveying and metering system is carried out, and then all metering supply valves 31 , 32) are simultaneously opened (84). Method according to claim 1, characterized in that the metering supply valves (31, 32) are only opened when the negative pressure (p) in the conveying and metering system is at least 5000 pascals. . Method according to claim 1, characterized in that the metering supply valves are opened after a first predetermined period. Method according to claim 2, characterized in that the first period ranges from 5 seconds to 10 seconds. Method according to any of the preceding claims, characterized in that the resuction (82) of the reducing agent is resumed after the metering supply valves (31, 32) are opened. . 6. Method according to claim 5, characterized in that the resuction (82) upon opening of the metering supply valves is carried out, at most, for a second, pre-determinable period. 7. Method according to claim 6, characterized in that the second period is at most 2 seconds. A computer program configured to execute each step of the method according to claim 1. A machine-readable storage medium storing the computer program according to claim 8. Electronic control device (70) configured to operate a conveying and metering system for a reducing agent solution of one or more SCR catalytic converters by a method according to claim 1.

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