DE102011076429A1 - Dosing system for catalytic reduction of combustion engine of commercial vehicle, has pump connected with dosing unit tank by suction line, where conveyance direction of pump is reversed by reversal rotation direction of pump motor - Google Patents

Abstract

The system has a pump (230) connected with a dosing unit tank (210) by a suction line (220). A metering valve (270) is connected with a filter (250) by a pressure line (260). A back suction line (290) is connected with a trunk line (240) at a connection point (291) between the pump and the filter, and is connected to a throttle (262) at another connection point (292) between a pressure sensor (261) and the pressure line, where a conveyance direction of the pump is reversed by reversal rotation direction of a pump motor. A non return valve (293) is arranged in the back suction line. Independent claims are also included for the following: (1) a method for operating a dosing system (2) a computer program comprising a set of instructions for performing a method for operating a dosing system.

Description

The present invention relates to a metering system, in particular for an SCR catalytic converter of an internal combustion engine. Furthermore, the present invention relates to a method for operating the dosing system according to the invention. Finally, the invention relates to a computer program that performs all the steps of the inventive method when the program runs on a computing device or a controller, and a computer program product with program code stored on a machine-readable carrier, for carrying out the method according to the invention, when the program a computing device or a controller is executed.

State of the art

Methods and apparatuses for operating an internal combustion engine, in particular in motor vehicles, are known, in the exhaust gas region of which an SCR catalytic converter (selective catalytic reduction) is arranged, which reduces the nitrogen oxides (NO _x ) contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent. As a result, the proportion of nitrogen oxides in the exhaust gas can be significantly reduced. For the course of the reaction ammonia (NH ₃ ) is required as a reducing agent, which is admixed to the exhaust gas. Therefore, NH ₃ or NH ₃ cleaving reagents are used as an additive. As a rule, an aqueous urea solution is used for this purpose, which is injected into the exhaust gas line in front of the SCR catalytic converter by means of a metering device. Such a urea solution is commercially available under the name AdBlue ^® . To store the urea solution as a reducing agent, a reducing agent tank is provided.

It is necessary to distribute the additive as evenly as possible and to meter it into the exhaust gas in particular with the highest possible degree of vaporization, since the catalysts are sensitive to the impact of still liquid additive and, if the degree of evaporation of the metered additive is too low, damage to the catalyst is to be feared. As metering or metering injectors are used which inject the liquid additive via a nozzle assembly under pressure in the exhaust system. The metering valve is always supplied with liquid additive during operation. Since the additive will typically be an aqueous solution and its volume expands upon freezing, it is important that the metering device, and particularly the metering valve, be protected against bursting and other damage at temperatures below the freezing point of the additive. For example, the freezing point of the aqueous urea solution AdBlue ^® is -11.5 ° C and thus in the range of temperatures that are practically reached in winter.

To counteract the risk of bursting, according to the prior art, the additive still present in the metering valve of the exhaust system is sucked back before the exhaust system is also stopped after the internal combustion engine has been switched off. In this case, the metering valve is actively deflated by additive so far that forming ice can not build up pressure, which leads to damage or destruction.

When the internal combustion engine is switched off, the return suction process must be actively initiated by a pump unit controlled by a control unit and requires a certain follow-up time before the exhaust system can be shut down. He is therefore only consuming to realize. A dosing system according to the prior art, which allows a Rücksaugvorgang is in 1 shown. The reducing agent tank 110 is by means of a suction line 120 with a 4/2 way valve 121 connected. This is with a diaphragm pump 130 connected. Furthermore, the 4/2 way valve 121 over a connecting line 140 with a main filter 150 connected. The main filter is by means of a pressure line 160 with the dosing valve 170 connected. The pressure line has a pressure sensor 161 , Besides branches from the pressure line 160 a return line 180 at a connection point 181 which is in the reducing agent tank 110 ends. The return line is with a return throttle 182 and a throttle check valve 183 fitted.

In some cases, for example in commercial vehicles for the transport of dangerous goods (so-called ADR vehicles), it is even imperative that the entire vehicle drive, including the exhaust system, can be stopped immediately by emergency stop. In the case of shutdown by emergency stop switch (so-called ADR switch), a return of additive from the metering valves is not possible. As a result, the metering valves of the exhaust system can remain filled with additive when the vehicle is stationary. In this way, damage due to freezing of additives can practically only be avoided if special ice pressure-resistant metering valves are installed. However, such ice pressure-resistant metering valves are technically complex and therefore expensive.

The not yet revealed German Patent Application No. 10 2010 031 660.1 describes a process for impulse sucking of reducing agent solution. During impulse back-suction, the air cushion generation system is available for a maximum of 1 second from the time the vehicle emergency stop switch is actuated. For this it is necessary to integrate a special hose line through their high volume expansion with pressure relief via a 2/2-way valve in the delivery module provides relaxation energy to accelerate the fluid column in the hose in the direction of the delivery module and on to the tank. After complete relaxation of the conduit wall of the pressure line there is a deceleration of the fluid column and due to the inertia of the fluid before the metering valve to build a negative pressure. This is used by using a suitable switching algorithm to suck by opening the metering valve during this vacuum enough air or exhaust gas in the metering valve.

Disclosure of the invention

Advantages of the invention

• a. einen Dosiermitteltank,
• b. eine Pumpe, welche mittels einer Ansaugleitung mit dem Dosiermitteltank verbunden ist,
• c. einen ersten Filter, welcher über ein Eisdruckkompensationselement verfügt, und der mittels einer Verbindungsleitung mit der Pumpe verbunden ist,
• d. ein Dosierventil, welches mittels einer Druckleitung mit dem Filter verbunden ist,
• e. einen Drucksensor, welcher in der Druckleitung angeordnet ist,
• f. eine Rücklaufleitung, welche an einem ersten Verbindungspunkt mit der Druckleitung verbunden ist und im Dosiermitteltank endet,
• g. ein erstes Rückschlagventil, welches in der Verbindungsleitung angeordnet ist,
• h. eine erste Drossel, welche zwischen dem Drucksensor und dem ersten Filter in der Druckleitung angeordnet ist,
• i. eine Rücksaugleitung, welche an einem zweiten Verbindungspunkt zwischen der Pumpe und dem ersten Filter mit der Verbindungsleitung verbunden ist und an einem dritten Verbindungspunkt zwischen dem Drucksensor und der ersten Drossel mit der Druckleitung verbunden ist, und
• j. ein zweites Rückschlagventil, welches in der Rücksaugleitung angeordnet ist.

The dosing system according to the invention, which is particularly suitable for an SCR catalytic converter of an internal combustion engine, allows and expands the sucking back of larger amounts of air and thus leads to a higher serial stability of the emergency stop Abstellfalles. It includes

• a. a dosing tank,
• b. a pump which is connected to the dosing agent tank by means of a suction line,
• c. a first filter which has an ice pressure compensating element and which is connected to the pump by means of a connecting line,
• d. a metering valve which is connected to the filter by means of a pressure line,
• e. a pressure sensor, which is arranged in the pressure line,
• f. a return line which is connected to the pressure line at a first connection point and ends in the dosing agent tank,
• G. a first check valve which is arranged in the connecting line,
• H. a first throttle, which is arranged between the pressure sensor and the first filter in the pressure line,
• i. a return suction pipe connected to the connection pipe at a second connection point between the pump and the first filter and connected to the pressure pipe at a third connection point between the pressure sensor and the first throttle, and
• j. a second check valve disposed in the return line.

The first check valve is designed to prevent the delivery of the dosing medium from the first filter towards the pump. The second check valve is arranged to inhibit the delivery of the dosing medium through the return line in the direction from the second connection point to the third connection point.

According to the invention, the dosing system for conveying and pressurizing the dosing means comprises a pump in which a direction of rotation can be effected by reversing the direction of rotation of the motor. This may be, for example, a gear pump. By reversing the direction of rotation, unlike a prior art metering system using a diaphragm pump, the system can be vented without a 4/2-way valve. A suck-back of the dosing agent is possible without any problems.

Due to the limited delivery rate of the pump, however, the large expansion volume of the Eisdruckkompensationselements in the first filter and the expansion volume of the pressure line can not be sucked back within a second to produce a Ansaugunterdruckes the metering valve. This is critical in that much less than a second is available for the recirculation process, since within this period of time, the metering valve must be open long enough to suck sufficient air or exhaust gas back into the metering valve.

In the dosing system according to the invention, the expansion volume of the Eisdruckkompensationselementes the first filter is therefore hydraulically decoupled from the Rücksaugvorgang to have to promote only the expansion volume of the pressure line back. As a result, the construction of a negative pressure on the metering valve for the suction of sufficient air or exhaust gas in selbiges in emergency failure within the available time is possible. The necessary volume flow capacity of the pump for the return feed can be reduced by this measure by about 75% compared to a conventional metering system, which uses a diaphragm pump and a 4/2 way valve. This means a significant cost reduction. In addition, the metering system according to the invention prevents leakage of the tank contents according to the principle of communicating tubes via valve leaks in applications in which the metering valve is geodetically lower than the Dosiermitteltank and the delivery module.

Preferably, a second filter is arranged in the suction line. This acts as a pre-filter for the dosing agent solution. As a result, coarse dirt and particles, which could damage the pump, kept away from the pump.

Furthermore, it is preferred that a second throttle is arranged in the return line. At zero dosage, the dosing system should preferably be maintained at operating pressure. The second throttle allows this the pump energy of the pump in the form of heat loss over a active recirculation, ie a return to the dosing tank, dissipate. In addition, the second throttle during suckback (see below) supports the pressure reduction of the hydraulically clamped between the first check valve and the first throttle volume.

In addition, it is possible to arrange a third check valve in the return line. The third check valve is arranged to inhibit the transport of the dosing medium from the dosing tank in the direction of the first connection point. The third check valve thus prevents the displacement of dosing from the dosing tank through the return line and the pressure line into the metering valve. Such a shift may occur in some embodiments of the invention when the pump is turned off. If a second throttle is arranged in the return line, the third check valve may be arranged either between the dosing agent tank and the second throttle, or it may alternatively be arranged between the second throttle and the first connection point.

The operation of the dosing system according to the invention can be divided into a delivery phase (A), a Rücksaugphase (B) and the Abstellfall (C).

During operation of the dosing system according to the invention in the delivery phase (A), the first check valve or filter check valve is opened during a dosing phase, the second check valve or pulse check valve is closed, and the dosing valve is opened. If no dosing occurs during the delivery phase (A), the dosing valve is closed, but the first check valve remains open and the second check valve remains closed. As a result, a volume flow generated by the pump can be discharged via the return line into the dosing agent tank, so that the system pressure in the dosing system is maintained even if no dosing of the dosing agent takes place. During the delivery of a dosing the first check valve is therefore always open and the second check valve is closed.

After completion of the delivery phase (A) by reversing the direction of rotation of the pump motor, a flow direction reversal of the pump causes and thus the Rücksaugphase (B) initiated. The first check valve closes and the second check valve opens. The activation of the metering valve is electrically controlled via a program sequence in a control unit. It is therefore not necessary to close the metering valve before or during the suck back process. However, should the metering be closed during the re-suction, the metering valve is opened to suck air or exhaust gas as soon as the pressure sensor detects falling below a certain pressure in the pressure line.

Preferably, after completion of a dosage by reversing the direction of rotation of the pump motor, a conveying direction reversal of the pump is effected at maximum speed in order to allow the dosing agent to suck back as quickly as possible.

If there is no emergency stop, the system voltage continues to be present and allows normal back suction while the metering valve is still open. Since no operation of the pump with maximum speed is necessary for this purpose, it is particularly preferred that after a certain period of time, the speed of the pump is reduced. It is most preferred after a period of one second, i. H. In the period during which system voltage would still be available during an emergency shutdown, the speed of the pump is reduced to normal speed. It is preferably sucked back until a defined part of the volume from the pressure line is fed back into the Dosiermitteltank. The amount of air in the metering valve, in the pressure line and the rest of the delivery module is thereby increased so that the maximum possible ice pressure protection is achieved by air filling. Then the dosing system can be completely turned off, so that the Abstellfall (C) is present.

The invention also relates to a computer program which carries out all the steps of the method according to the invention for operating the dosing system when the program is run on a computing device or a control unit, and a computer program product with program code which is stored on a machine-readable carrier for carrying out the method according to the invention, when the program is run on a computing device or controller.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description:

1 shows a conventional dosing system according to the prior art.

2 shows an embodiment of the dosing system according to the invention.

3 shows the time course of the pressure at the pressure sensor, the metering valve and the first filter of a metering system according to the invention during the first second of a Rücksaugvorgangs with a maximum pump speed of 12,000 revolutions per minute.

4 shows the time course of in a metering system according to the invention during the first second of a Rücksaugvorgangs with a pump speed of 12,000 revolutions per minute maximum sucked amount of air.

5 shows the time course of the pump speed in a metering system according to the invention during the first second of a Rücksaugvorgangs with a pump speed of up to 12,000 revolutions per minute.

6 shows the time course of the pressure at the pressure sensor, the metering valve and the first filter of a metering system according to the invention during the first second of a Rücksaugvorgangs with a pump speed of up to 6,000 revolutions per minute.

7 shows the time course of in a metering system according to the invention during the first second of a Rücksaugvorgangs with a maximum pump speed of 6,000 revolutions per minute sucked amount of air.

8th shows the time course of the pump speed in a metering system according to the invention during the first second of a Rücksaugvorgangs with a pump speed of at most 6,000 revolutions per minute.

Embodiments of the invention

In 2 an embodiment of the metering system according to the invention is shown. This is suitable for the SCR catalytic converter of the engine of an ADR vehicle. A reducing agent tank 210 , which contains AdBlue ^® , is by means of a suction line 220 with a gear pump 230 connected. In the intake pipe 220 is a pre-filter 221 arranged. A connection line 240 connects the gear pump 230 with a main filter 250 , The main filter 250 has an ice pressure compensation element. In the connection line 240 is a first check valve 241 The promotion of AdBlue ^® from the main filter 250 in the direction of the gear pump 230 in derogation. The main filter 250 is by means of a pressure line 260 with a metering valve 270 connected. In the pressure line 260 is a pressure sensor 261 arranged. Between the main filter 250 and the pressure sensor 261 is a first throttle 262 arranged. Between the main filter 250 and the first throttle 262 branches a return line 280 at a first connection point 281 from the pressure line 260 from. The return line 280 contains a second throttle 282 and ends in the dosing tank 210 , Between the dosing tank 210 and the second throttle 282 is a third check valve 283 arranged. The third check valve 283 is set up so that it can transport the dosing medium through the return line 280 from the dosing tank 210 in the direction of the first connection point 281 in derogation. A return line 290 connects a second connection point 291 on the connecting line 240 between the pump 230 and the first check valve 241 with a third connection point 292 at the pressure line 260 between the pressure sensor 261 and the first throttle 262 , In the return line 290 is a second check valve 293 The delivery of AdBlue ^® through the return line 290 in the direction of the second connection point 291 to the third connection point 292 in derogation.

During the normal dosing and conveying process, the gear pump sucks 230 over the pre-filter 221 AdBlue ^® from the reducing agent tank 210 and brings it to the required system pressure. The second check valve 293 is closed, leaving AdBlue ^® through the first check valve 241 through the pressure-side main filter 250 flows. The ice pressure compensation element in the pressure-side filter 250 is compressed and absorbs a corresponding volume of AdBlue ^® . After the filter 250 A certain amount of AdBlue ^{® flows} through the second throttle 282 and return line 280 into the reducing agent tank 210 back. The amount required for the dosage flows through the first throttle 262 , runs on the pressure sensor used to control the system pressure 261 over and over the pressure line 260 to the metering valve 270 directed. Here the AdBlue ^{® is} metered into the exhaust gas line as required.

If the driver of the ADR vehicle actuates the vehicle emergency stop, the entire vehicle system is de-energized after one second has elapsed. Within this time, sufficient freeze protection for the components is produced according to the invention. The AdBlue ^® is sucked back by immediately reversing the direction of rotation of the gear pump 230 with maximum speed with closed metering valve 270 , By returning the AdBlue ^® to the reducing agent tank 210 over the pre-filter 221 and the suction line 220 the system pressure decreases. The first check valve 241 closes, the expansion volume of the ice pressure compensation body in the main filter 250 can only have the second throttle 282 and return line 280 into the reducing agent tank 210 and to a lesser extent over the first throttle 262 relax into the sucked back hydraulic volume. By the arrangement of the first check valve 241 and first throttle 262 becomes the expansion volume of the ice pressure compensating element in the main filter 250 hydraulically isolated and relaxed slowly over the second throttle 282 and the return line 280 into the reducing agent tank 210 , The over the first throttle 262 introduced amount in the branch to be emptied is very low. Through this decoupling of the expansion volumes of Eisdruckkompensationselement in the main filter 250 and pressure line 260 becomes the return power of the gear pump required until sufficient vacuum is reached 230 reduced to a minimum. That in the pressure line 260 stored hydraulic volume now flows through the second check valve 293 in the direction of the gear pump 230 and including the small inflowing volume flow from the ice pressure compensating element of the main filter 250 over the first throttle 262 fed back into the reducing agent tank. After a while, the gear pump has 230 the entire volume of expansion via the suction line 220 back promoted and can now build the necessary vacuum. Once from the pressure sensor 261 a sufficient negative pressure is detected, the metering valve 270 controlled and air or exhaust gas is sucked. The sucked back amount of gas volumes is for the ice pressure protection of the metering valve 270 sufficient. The volume in the main filter 250 , which is at a higher pressure level than the volumes of the pressure line 260 flows through the second throttle within one second 282 and the first throttle 262 until pressure equalization. After one second has passed, the emergency back-suction is completed and thus is the necessary basic protection for the non-pressure-proof metering valve 270 produced.

The metering system according to the invention can not distinguish between the emergency stop case and a normal vehicle parking case. If there is no emergency stop case, however, the system voltage still remains and allows a normal back suction while the metering valve is still open 170 , This is done with normal speed of the gear pump 230 sucked back until a defined part of the volume from the pressure line 260 into the reducing agent tank 210 is promoted back. The amount of air in the metering valve 270 , in the pressure line 260 and in the rest of the delivery module is thereby increased such that the maximum possible ice pressure protection is achieved by air filling. Then the dosing system can be completely switched off.

The dosing system according to the invention was tested for functionality by means of 1D flow simulation with the tool AmeSim (LMS Imagine Lab). The results for suck back with a maximum pump speed of 12,000 revolutions per minute, each for a simulation period of one second, are in the 3 to 5 shown. 3 shows the time course of the pressure P (in bar, 1 bar = 10 ⁵ Pascals) at the pressure sensor 261 , on the dosing valve 270 and at the first filter 250 , From the different pressure levels, the effectiveness of the metering system according to the invention is clearly visible. 4 shows the time course of the per minute in the dosing sucked air volume V_a. After one second, a total of 13 cm ³ gas volume was sucked in. This is completely sufficient for a reliable ice protection. 5 shows the time course of the pump speed n.

The simulation was repeated for a maximum pump speed of 6,000 revolutions per minute. The results are in the 6 to 8th shown. 6 it can be seen that a total of 10.5 cm ³ gas volume was sucked in after one second. While this is less than a maximum pump speed of 12,000 revolutions per minute, it is still sufficient for reliable ice pressure protection. Thus, the dosing system according to the invention can be used reliably even if only low pump speeds can be achieved.

The metering system according to the invention thus makes it possible to ensure reliable ice pressure protection in ADR vehicles even if no ice-pressure-resistant metering valve is used.

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 102010031660 [0007]

Claims (10)

Dosing system, in particular for an SCR catalytic converter of an internal combustion engine, comprising a. a dosing agent tank ( 210 b. a pump ( 230 ), which by means of a suction line ( 220 ) with the dosing agent tank ( 210 ), c. a first filter ( 250 ), which has a Eisdruckkompensationselement, and by means of a connecting line ( 240 ) with the pump ( 230 ), d. a metering valve ( 270 ), which by means of a pressure line ( 260 ) with the filter ( 250 ), e. a pressure sensor ( 261 ), which in the pressure line ( 260 ), f. a return line ( 280 ), which at a first connection point ( 281 ) with the pressure line ( 260 ) and in the dosing tank ( 210 ), characterized in that the dosing system further comprises: g. a first check valve ( 241 ), which in the connecting line ( 240 ), h. a first throttle ( 262 ), which between the pressure sensor ( 261 ) and the first filter ( 250 ) in the pressure line ( 260 ), i. a return line ( 290 ), which at a second connection point ( 291 ) between the pump ( 230 ) and the first filter ( 250 ) with the connecting line ( 240 ) and at a third connection point ( 292 ) between the pressure sensor ( 261 ) and the first throttle ( 262 ) with the pressure line ( 260 ), and j. a second check valve ( 293 ), which in the return line ( 290 ) and that at the pump ( 230 ) by reversing the direction of rotation of the pump motor, a conveying direction reversal can be effected. Dosing system according to claim 1, characterized in that it is in the pump ( 230 ) is a gear pump. Dosing system according to claim 1 or 2, characterized in that in the suction line ( 220 ) a second filter ( 221 ) is arranged. Dosing system according to one of claims 1 to 3, characterized in that in the return line ( 280 ) a second throttle ( 282 ) is arranged. Method for operating the dosing system according to one of claims 1 to 4, characterized in that A. during the delivery of a dosing the first check valve ( 241 ), and the second check valve ( 293 ) is closed, and B. after completion of the conveying by reversing the direction of rotation of the pump motor, a direction of flow reversal of the pump ( 230 ), the first check valve ( 241 ) is closed, and the second check valve ( 293 ) is opened, wherein the metering valve ( 270 ) is opened as soon as the pressure sensor ( 261 ) falling below a certain pressure in the pressure line ( 260 ) detected. A method according to claim 5, characterized in that after completion of the conveying by reversing the direction of rotation of the pump motor, a conveying direction reversal of the pump ( 230 ) is effected at maximum speed. A method according to claim 6, characterized in that after completion of the conveying after a certain period, the speed of the pump ( 230 ) is reduced. A method according to claim 7, characterized in that after completion of the conveying after a period of one second, the speed of the pump ( 230 ) is reduced to normal speed. Computer program that performs all the steps of a method according to one of claims 5 to 8, when the program runs on a computing device or a controller. Computer program product with program code, which is stored on a machine-readable carrier, for performing a method according to one of claims 5 to 8, when the program is executed on a computing device or a control device.

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