Method and apparatus for metering aqueous urea solution

Abstract

The invention relates to a method for controlling a delivery device for an aqueous urea solution in a motor vehicle, the delivery device having a tank, a suction line, a pump, a pressure line and an injector, wherein the aqueous urea solution can be delivered from the tank along the suction line past the pump, the pressure line and towards the injector, wherein the method is designed to carry out a flushing process of at least the pressure line, wherein the pump is operated against its usual delivery direction during the flushing process and the injector is closed in a first phase of the method, wherein the pump is operated for a duration of operation t1 and at a rotational speed n1 during the first phase of the method. The invention also relates to a device for carrying out the method.

Description

Technical Field

[0001] This invention relates to a method for controlling the delivery of an aqueous urea solution in a motor vehicle, the delivery device comprising a storage tank, a suction line, a pump, a pressure line, and an injector, wherein the aqueous urea solution can be delivered from the storage tank along the suction line, through the pump, and the pressure line toward the injector, wherein the method is designed to perform a flushing process on at least the pressure line, wherein during the flushing process the pump is operated against its normal delivery direction and the injector is shut off in a first phase of the method, wherein during the first phase of the method the pump is operated at a rotational speed n1 for an operating duration t1. The invention also relates to an apparatus for implementing the method. Background Technology

[0002] Globally, many countries have enacted laws that set upper limits on the content of certain substances in internal combustion engine exhaust. These substances are mostly those undesirable for release into the environment. One such substance is nitrogen oxides (NOx), whose share in exhaust cannot exceed legal limits. Due to constraints such as the design of internal combustion engines for optimal fuel efficiency, avoiding NOx emissions within the engine while reducing the NOx share in exhaust is only partially applicable, thus requiring exhaust aftertreatment to comply with relatively low limits. Selective catalytic reduction (SCR) of NOx has proven advantageous. This SCR method requires a nitrogen-containing reducing agent. The use of ammonia (NH3) as a reducing agent has proven to be a possible alternative. Based on its chemical properties and legal regulations in many countries, ammonia is generally not stored as pure ammonia, as this would cause problems, particularly in motor vehicles or other mobile applications. Instead of storing the reducing agent itself, reducing agent precursors are often stored and carried. Reducing agent precursors are specifically understood as materials capable of dissociating the reducing agent or that can be chemically converted into a reducing agent. For example, ammonia-urea is a reducing agent precursor.

[0003] An aqueous solution of ammonia, i.e., urea, is carried in a storage tank and delivered to the exhaust system in precisely measured quantities using suitable conveying equipment. For this purpose, the aqueous ammonia solution is conveyed along a pressure line from the conveying equipment toward an injector. Finally, the urea solution is introduced into the exhaust system through the injector, where it is thermally converted into ammonia and water for subsequent reduction of nitrogen oxides contained in the exhaust gas.

[0004] In addition to other functions, a flushing function is implemented in the conveying equipment to flush the conveying pipeline and remove any possible residues of the ammonia solution. For this purpose, for example, when the ejector is closed, a negative pressure is generated in the pressure pipeline by running the pump of the conveying equipment against the normal conveying direction. After creating negative pressure in the pressure pipeline, the ejector is opened, causing the ammonia solution still in the pressure pipeline to be drawn back towards the storage tank. Furthermore, the flushing can be assisted by running the pump.

[0005] A drawback of existing solutions is that the flushing process is not variable and therefore cannot be adjusted due to changes in the entire system, such as pump wear. Summary of the Invention

[0006] Therefore, the object of the present invention is to provide a method that allows the flushing process to be adjusted based on equipment condition parameters, such as pump aging or pump delivery power. Furthermore, the object of the present invention is to provide an apparatus for implementing the method.

[0007] The methodological objective is achieved by a method having the features of claim 1.

[0008] One embodiment of the present invention relates to a method for controlling the delivery of an aqueous urea solution in a motor vehicle, the delivery device having a storage tank, a suction line, a pump, a pressure line, and an injector, wherein the aqueous urea solution can be delivered from the storage tank along the suction line, through the pump, and the pressure line toward the injector, wherein the method is designed to perform at least a flushing process on the pressure line, wherein during the flushing process the pump is operated against its normal delivery direction and the injector is shut off in a first phase of the method, wherein during the first phase the pump is operated at a rotational speed n1 for an operating duration t1, wherein in the first phase a negative pressure p1 is generated in the pressure line that is directly related to the operating duration t1 and the rotational speed n1, wherein the operating duration t1 and the rotational speed n1 are determined according to a calibration process performed during the initial commissioning of the device, and the operating duration and rotational speed, as well as the resulting negative pressure p1, are stored in the device's memory, wherein in a second phase of the method the injector is turned on and the pump continues to operate against its normal delivery direction.

[0009] The pump's operating duration and rotational speed determine the volume of fluid that can be delivered by the pump. Increased rotational speed or extended operating duration results in a higher delivery volume. Because the pump removes the urea solution and any air that may be present in the pressure line from the closed ejector at the end of the pressure line during the first stage, a negative pressure is created in the pressure line. The longer the pump runs and the faster it rotates, the higher the resulting negative pressure can become.

[0010] Characteristics such as the compressibility of the fluid in the pressure line, the internal volume of the pressure line, and the sealing performance of the equipment also affect the maximum achievable negative pressure. For a specific piece of equipment, the volume of the pressure line and the sealing performance of the equipment can be considered constant, making these factors less important for generating negative pressure during the equipment's service life. The formation of negative pressure is decisively determined by the pump's rotational speed and the duration of its operation. Other important parameters influencing the formation of negative pressure include variations in pump performance over its service life and performance differences between essentially identical pumps due to unavoidable manufacturing tolerances.

[0011] In known devices, the negative pressure generated in the first stage can be accurately predicted by the pump's operating duration and speed, as the formation of negative pressure is essentially influenced by these two parameters. However, the pressure in the pressure line can be determined / obtained significantly more accurately by a pressure sensor, preferably one capable of accurately determining the pressure in the pressure line at any time. Preferably, the pressure sensor is designed not only to detect the negative pressure formed in the first stage but also to detect overpressure, such as that formed when a urea solution is injected into the exhaust system via an injector.

[0012] The flushing process of the equipment is divided into two stages. In the first stage, the injector is shut off, and the pump flows against its normal delivery direction. The normal delivery direction of the pump is the direction in which the urea solution enters the pressure line from the storage tank and is delivered to the injector. The term "against the normal delivery direction" means that the urea solution is delivered from the pressure line toward the storage tank. This is achieved by reversing the direction of rotation of the pump stages.

[0013] Because the injector is shut off in the first stage, the pump can deliver the urea solution from the pressure line toward the storage tank and also deliver air from the pressure line. However, because no additional fluid can flow into the pressure line through the injector, a negative pressure is created in the pressure line. This is similar to the principle that an air pump opens when a valve opening is blocked.

[0014] In the second stage, the ejector is finally opened, allowing fluid to flow from the exhaust system into the pressure line. The pump preferably continues to pump in the opposite direction to its normal delivery flow during this second stage. By allowing fluid to flow into the pressure line and the pump's continued pumping action, the fluid contained in the pressure line—which can be not only air but also an aqueous solution of urea—is being pumped toward the storage tank. The stronger the negative pressure before the ejector is opened and the faster and longer the pump operates, the more fluid is pumped from the pressure line toward the storage tank.

[0015] Preferably, the pressure line is purged of fluid, while the suction line and pump, particularly the pump stage, are not completely purged of fluid.

[0016] Preferably, the pump's operating duration t1 and rotational speed n1 are determined according to the values ​​of the corresponding specialized equipment in a so-called "end of line" check. This check is performed after the equipment is installed in the vehicle to verify functionality. This check determines how long and how fast the pump must operate to generate the desired negative pressure p1. The determined values ​​of operating duration t1 and rotational speed n1 are stored in the system's memory. Therefore, it is determined and stored that the pump, in a known equipment configuration, must operate for how long and how fast in its delivery state to generate the desired negative pressure.

[0017] Because the equipment also undergoes some aging during its service life, it is uncertain whether the same desired negative pressure will be achieved even in aged equipment within the initially defined operating duration at a fixed speed. Pumps, in particular, will experience aging. Due to wear or contamination, the pump's delivery capacity may be affected. Therefore, with the same speed and operating duration, the delivery rate can be reduced. To compensate for this effect, the method according to the invention must be designed accordingly.

[0018] Particularly advantageous is that a flushing process is performed during at least one start-up process following the initial commissioning of the pump, wherein a negative pressure p2 generated in the pressure line during the first stage of the flushing process is detected and compared with a negative pressure p1 obtained by means of the running duration t1 and rotational speed n1 stored in memory.

[0019] The flushing process can be performed once, at fixed intervals, or during each start-up of the pump or equipment. Here, the negative pressure is determined based on the values ​​of the running duration and rotational speed stored in memory, which are derived under these framework conditions in the pressure lines.

[0020] No adjustment is necessary as long as the generated negative pressure p2 corresponds to the initially desired negative pressure p1. However, if the negative pressure p2 should be smaller, and therefore less negative pressure is generated while the pump's operating conditions remain unchanged, then corresponding adjustments must be made according to the method of the invention in order to enable the operation of the equipment.

[0021] Advantageously, a comparison of negative pressures p1 and p2 is performed, wherein a correction coefficient K1 is calculated based on the deviation between negative pressures p1 and p2, and the running duration is adjusted from value t1 to value t2, and / or the rotational speed is adjusted from value n1 to value n2 using this correction coefficient.

[0022] The detection and comparison of negative pressure can preferably be performed in a computing unit, such as a controller.

[0023] If the negative pressure p2 is less than the negative pressure p1, then it is necessary to extend the operating duration and / or increase the rotational speed so that the negative pressure p2 approaches the level of p1 and ideally is the same as that negative pressure p1. Therefore, according to the invention, the pump's operating parameters are converted by comparing with the determined correction coefficient K1 and thus the new operating parameters are stored in memory for continued operation.

[0024] During future flushing processes, comparisons can be made between the negative pressure p1 and the operating parameters based on that negative pressure, or between the negative pressure p2 achieved after calibration.

[0025] This specifically involves operating parameters, such as operating duration and rotational speed. Since changes in equipment that cause negative pressure variations are usually irreversible, it follows that the negative pressure p2 generated using the newly discovered operating parameters t2 and n2 can only be achieved in the future by further adjusting the operating parameters.

[0026] A preferred embodiment is characterized in that, during the second phase of the method, the pressure lines are flushed by the generated negative pressure and the continuous operation of the pump against its normal delivery direction, wherein fluid located in the pressure lines is delivered towards the storage tank via the suction line. Preferably, the pressure lines are emptied of fluid as much as possible during this process. However, it is desirable that not the entire device, and particularly not the suction line and pump stage, be completely emptied to avoid dry operation of the pump.

[0027] Preferably, a correction coefficient K1 calculated based on the deviation between negative pressure p1 and negative pressure p2 is used to adjust the pump's operating duration t3 and / or rotational speed n3 during the second stage of the method.

[0028] It may also be necessary, given the aging and wear previously described in the equipment, to increase the operating duration and speed in the second stage in order to output a greater volume of liquid from the pressure lines.

[0029] Furthermore, it is advantageous to connect a third stage after the first and second stages, in which the pump is operated in its usual delivery direction and thus overpressure is generated in the pressure line, wherein the pump's operating duration t4 and / or rotational speed n4 are changed from the original values ​​using a calculated correction factor K1 in the third stage.

[0030] The third stage involves establishing pressure in the pressure pipeline. Through the operation of the pump, the urea solution is pumped from the storage tank into the pressure pipeline in its usual delivery direction.

[0031] Because pump wear has the same effect on delivery power in the pump's normal delivery direction as it does against the pump's normal delivery direction, the operating duration t4 and / or speed n4 are also adjusted by a correction factor K1 to ensure sufficient overpressure is established in the pressure line.

[0032] Furthermore, it is advantageous to connect a fourth stage after the first and second stages of the method, wherein the third stage follows the fourth stage or the method ends, wherein during the fourth stage the injector is shut off and the pump is run against its usual delivery direction at a speed n5 for a running duration t5.

[0033] The fourth stage described here corresponds to the first stage of the already described flushing process. A negative pressure p5 is established in the pressure line when the ejector is closed. For this purpose, the pump is run against its normal delivery direction at a speed n5 for a duration t5.

[0034] It is also appropriate to determine the negative pressure p5 in the pressure line and compare it with the negative pressure p1 stored in the memory, wherein the ratio of negative pressure p5 to negative pressure p1 allows direct deduction of the amount of remaining air and the amount of remaining urea solution in the pressure line.

[0035] The comparison between the negative pressure p5 generated in the fourth stage and the negative pressure p1 stored in memory allows for the direct deduction of the amount of urea solution contained in the pressure line and the amount of air contained therein. This is directly derived from the physical properties of the gas and liquid, where the gas—in this case, air—has higher compressibility than the liquid. By the ratio between the two negative pressures, the amount of fluid in the pressure line can be accurately deduced under other known conditions.

[0036] With the same pump speed and operating time, the achievable negative pressure in the pressure line depends on the ratio of liquid to gas in the pressure line. In the ideal extreme case, the pressure line is, for example, completely filled with liquid. In the worst extreme case, the pressure line is completely filled with gas.

[0037] Now, for a dedicated pressure pipeline with a given length and volume, the maximum negative pressure achievable under specified operating conditions can be determined experimentally for various liquid-to-gas ratios. This determined value can be stored in memory, allowing the corresponding gas-to-liquid ratio to be deduced subsequently during operation from the negative pressure p5 determined in the pressure pipeline.

[0038] Furthermore, it is advantageous to calculate the actual amount of urea solution remaining in the pressure line after the fourth stage, using negative pressure p5, pump operating duration t5, pump speed n5, injector static flow rate, and internal volume of the pressure line for this purpose.

[0039] Preferably, the amount of urea solution actually located in the pressure line is calculated by taking into account the maximum volume of the pressure line, the static flow rate of the ejector, and the time the ejector is open. The maximum line volume is known. Within a specified time, a specified fluid volume can flow through the ejector, based on the static flow rate dedicated to the ejector.

[0040] As the gas is pumped back towards the storage tank, it flows into the pressure line through an open injector. This gas displaces the liquid in the pressure line. Given the known volume of the line and the amount of gas drawn into the pressure line through the injector, the volume of liquid remaining in the pressure line can be calculated.

[0041] Because the amount of liquid in the pressure line at the beginning of the process can only be transported out of the pressure line towards the storage tank, given the length and volume of the pressure line, and the amount of gas drawn into the pressure line, it is possible to deduce how far the gas is drawn into the pressure line and, consequently, where the phase boundary between the gas and liquid is in the pressure line.

[0042] Furthermore, it is appropriate to compare the amount of urea solution remaining in the pressure line determined by comparing negative pressure p5 and p1 with the amount of urea solution remaining in the pressure line calculated according to the aforementioned method, wherein a correction coefficient K2 is generated when a fixed maximum difference between the two amounts is exceeded, and the duration of the first and / or second stages of the method is corrected by the correction coefficient.

[0043] With the help of the correction factor K2, the overall length of the flushing process, consisting of the first and second stages, is extended. This results in more fluid being delivered from the pressure line overall.

[0044] Based on calculations of the amount of fluid still in the pressure line, and particularly the amount of urea solution, it is possible to determine how far the urea solution within the pressure line has been drawn towards the pump. This is because, given the known volume of the pressure line, the amount of urea solution, the amount of air in the pressure line, and the position of the liquid within the pressure line are directly related to each other. This, in particular, prevents the urea solution from being drawn out of the pressure line to such an extent that the pump stage becomes dry and thus could lead to dry operation of the pump.

[0045] Furthermore, knowing the precise amount of air present in the pressure line allows for optimization of the so-called priming process, in which air contained in the pressure line is forced out of the pressure line by a pump operating in its normal delivery direction with the ejector open. This allows for improved metering strategies because the duration for which a specified amount of air is delivered from the pressure line can be precisely determined based on the pump's known effective power. By knowing the air present in the pressure line and the time required to deliver air from it, it is possible to precisely determine when to vent the pressure line and begin actually metering the urea solution into the venting system.

[0046] It is also appropriate to perform the comparison of negative pressure p1 and p2 as follows, wherein a correction coefficient K3 is calculated based on the deviation between negative pressure p1 and negative pressure p2, and then the correction coefficient K3 is used to adjust the running duration t4 or speed n4 in the third stage.

[0047] Dry operation of the pump can be identified in particular by comparison because a significant negative pressure cannot be established in the pressure line during dry operation. If dry operation is identified, a correction factor K3 is applied to increase the operating duration t4 and / or speed n4 in the third stage, thereby ensuring sufficient fluid is drawn from the tank and thus adequate venting of the pressure line, and therefore the desired overpressure can be generated in the pressure line.

[0048] The objective in terms of the device is achieved by the device having the features of claim 1.

[0049] One embodiment of the present invention relates to an apparatus for conveying an aqueous urea solution in a motor vehicle, the apparatus having a storage tank, a suction line, a pump, a pressure line, and an injector, wherein the aqueous urea solution can be conveyed from the storage tank along the suction line through the pump and the pressure line toward the injector, wherein the apparatus can be used to perform the method according to the preceding claims, wherein the apparatus has means for detecting the pressure in the pressure line.

[0050] Advantageous improvements of the invention are described in the dependent claims.

Claims

1. A method for controlling the delivery of an aqueous urea solution in a motor vehicle, the delivery equipment comprising a storage tank, a suction line, a pump, a pressure line, and an injector, wherein the aqueous urea solution is delivered from the storage tank along the suction line, through the pump, and the pressure line toward the injector, the method being designed to perform at least a flushing process of the pressure line, wherein, The operating duration t1 and rotational speed n1 are determined according to the calibration process performed during the initial commissioning of the device. During the flushing process, the pump is run against its normal delivery direction and the injector is shut off in the first phase of the method. During the first phase of the method, the pump is run at the rotational speed n1 for the operating duration t1. In the first phase, a desired negative pressure p1 directly related to the operating duration t1 and the rotational speed n1 is generated in the pressure line, and the operating duration t1, the rotational speed n1, and the resulting desired negative pressure p1 are stored in the device's memory. In the second phase of the method, the injector is turned on and the pump continues to run against its normal delivery direction.

2. The method according to claim 1, characterized in that, A flushing process is performed during at least one start-up process following the initial commissioning of the pump, wherein a detected negative pressure p2 generated in the pressure line during the first stage of the flushing process is detected and compared with a desired negative pressure p1 obtained by means of the running duration t1 and rotational speed n1 stored in memory.

3. The method according to claim 2, characterized in that, A comparison is made between the desired negative pressure p1 and the detected negative pressure p2. A correction coefficient K1 is calculated based on the deviation between the desired negative pressure p1 and the detected negative pressure p2. The operating duration is adjusted from value t1 to value t2, and / or the rotational speed is adjusted from value n1 to value n2 using this correction coefficient.

4. The method according to claim 2 or 3, characterized in that, During the second phase of the method, the pressure line is flushed by the generated negative pressure and the continuous operation of the pump against its normal delivery direction, wherein the fluid in the pressure line is delivered to the storage tank via the suction line.

5. The method according to claim 4, characterized in that, The correction coefficient K1, calculated based on the deviation between negative pressure p1 and negative pressure p2, is used to adjust the pump's operating duration t3 and / or rotational speed n3 during the second stage of the method.

6. The method according to claim 5, characterized in that, A third stage is added after the first and second stages, in which the pump is operated in its normal delivery direction and thus overpressure is generated in the pressure line, and the pump's operating duration t4 and / or speed n4 are changed from the original values ​​of the pump operating in its normal delivery direction according to a calculated correction factor K1.

7. The method according to claim 6, characterized in that, A fourth stage is added after the first and second stages of the method, wherein the third stage follows the fourth stage or the method ends after the fourth stage. During the fourth stage, the injector is shut off and the pump is run against its normal delivery direction at a speed of n5 for a running duration of t5.

8. The method according to claim 7, characterized in that, The negative pressure p5 in the pressure line during the fourth stage is determined based on the rotational speed n5 and the running duration t5, and this negative pressure p5 is compared with the expected negative pressure p1 stored in the memory. The ratio of negative pressure p5 to expected negative pressure p1 allows direct inference of the amount of air remaining in the pressure line and the amount of urea solution remaining in the pressure line.

9. The method according to claim 8, characterized in that, After the fourth stage, the actual amount of urea solution remaining in the pressure line is calculated, whereby the negative pressure p5, the pump operating duration t5, the pump speed n5, the static flow rate of the ejector, and the internal volume of the pressure line are used for this purpose.

10. The method according to claim 9, wherein, The amount of urea solution remaining in the pressure line, determined by comparing negative pressure p5 with the expected p1, is compared with the amount of urea solution remaining in the pressure line calculated after the fourth stage. A correction factor K2 is generated when the determined maximum difference between the two amounts is exceeded. This correction factor is used to correct the duration of the first and / or second stages of the method.

11. The method according to claim 6, characterized in that, A comparison is made between the desired negative pressure p1 and the detected negative pressure p2. A correction coefficient K3 is calculated based on the deviation between the desired negative pressure p1 and the detected negative pressure p2. Then, the correction coefficient K3 is used to adjust the running duration t4 or the rotational speed n4 in the third stage.

12. An apparatus for conveying an aqueous urea solution in a motor vehicle, the apparatus comprising a storage tank, a suction line, a pump, a pressure line, and an injector, wherein, A urea aqueous solution can be delivered from a storage tank along a suction line through a pump and a pressure line toward an injector, and the method according to any one of the preceding claims can be performed using the device, which has a means for detecting the pressure in the pressure line.