Method for operating a conveying and dosing system

Abstract

Method for operating a conveying and metering system, which is designed for conveying a liquid medium from a tank (3) and for metering the medium via a pressure line (4) by means of at least one metering unit (7), wherein the system comprises at least one conveying pump (10) and at least one device for returning the medium, in particular a return pump (20) and / or a switching valve (200) for a return flow, wherein after the system is switched off, a return of medium from the pressure-side part of the system is provided, characterized in that after and / or during the return of medium, a flushing of the return path is carried out with the metering unit (7) closed by activating the conveying pump (10) and by activating the device for returning the medium, wherein the return of medium after the system is switched off and the flushing of the return path are carried out alternately.

Description

[0001] The present invention relates to a method for operating a conveying and metering system, which is designed for conveying a liquid medium from a tank and for metering the medium via a pressure line by means of at least one metering unit. The system comprises at least one conveying pump and at least one device for returning the medium. State of the art

[0002] Methods and devices for operating an internal combustion engine, particularly in motor vehicles, are known in which an SCR (Selective Catalytic Reduction) catalyst is arranged in the exhaust system. This catalyst reduces the nitrogen oxides (NOx) contained in the exhaust gas of the internal combustion engine to nitrogen in the presence of a reducing agent. This significantly reduces the proportion of nitrogen oxides in the exhaust gas. Ammonia (NH3) is required for the reaction and is added to the exhaust gas. An aqueous urea solution is typically used to supply the ammonia; this solution is injected into the exhaust stream upstream of the SCR catalyst by means of a metering device.

[0003] The urea solution is typically stored in a urea solution tank within the vehicle. A conveying and metering system is generally used to pump the urea solution. This system includes the urea solution tank, a pumping unit, a pressure line, a metering unit, the necessary sensors, and an electronic control unit. Hereinafter, the entire conveying and metering system, which specifically includes the tank, pump(s), valves, lines, metering device, sensors, and control unit, is referred to as the "system." The pumping system, in the narrower sense, primarily comprises the pump(s), any pulsation dampeners, lines, and valves.

[0004] A key component of the delivery and metering system is generally a delivery pump that draws the desired and required quantity of urea solution from the tank and feeds it into the pressure line within a specific system pressure range. The metering unit, which may include one or more metering valves, then injects the urea solution into the exhaust system as needed.

[0005] To prevent damage to the sensitive components of this system from ice pressure at low temperatures, it is generally designed so that the urea solution is drawn back from the dosing unit into the tank after the engine or vehicle is switched off. For this purpose, the feed pump can be equipped with a switching unit, such as a 4 / 2-way valve. Other systems utilize a separate return channel with a switching valve. Newer systems may have a separate return pump that allows the fluid to be drawn back from the dosing unit and, if necessary, from the pressure line.

[0006] During the emptying of the entire pressure-side system or a portion thereof, particularly the pressure line, the metering valve, and potentially the outlet side of the pumping device, warm or hot medium can enter and remain in the return path and the tank unit / support structure. This can lead to significant heating in these areas. The resulting high temperatures can damage the components and parts installed there. Furthermore, the heating of these components creates the problem that the temperatures within the pumping system, which are often used for modeling various data, change and are not recorded. Consequently, temperature and / or indirect pressure models, for example, operate with incorrect input values.The invention is therefore based on the objective of protecting the components in this area and reducing the load due to the temperature effect of the previously drawn-back medium, as well as solving the problem of the increased and uncaptured temperature values ​​after a backflow as input variables for various model calculations.

[0007] DE 10 2010 004 201 A1 relates to a method for operating a conveying device (1) for conveying a reducing agent from a reducing agent tank (2) into an exhaust gas treatment device (3) of an internal combustion engine (4) of a motor vehicle (5), wherein a venting process (22) of the conveying device (1) takes place at least intermittently during the operation of the internal combustion engine (4). In the method according to the invention, a venting process (22) is first registered. Subsequently, a timer (6) with a preset time interval (16) and / or a mass flow adder (25) with a preset total mass flow (26) is activated. When the preset time interval (16) and / or the preset total mass flow (26) is reached, a venting process (22) is then carried out. This eliminates the need for monitoring the conveying device with a pressure sensor.

[0008] DE 10 2005 002 318 A1 discloses a method and a device for post-treatment of exhaust gases of an internal combustion engine using a reaction agent, in particular a reducing agent, to be introduced into the exhaust gases, wherein the reaction agent is conveyed from a reaction agent container (1) to a metering device (7) by means of a conveying device (4), in particular a pump;80), in particular a metering valve, so that after opening the metering device the reaction agent can be metered into an exhaust line of the internal combustion engine (metering operation 810), wherein reaction agent can be conveyed back from the conveying device (4) to the reaction agent container (1) via a return line (12), wherein the reaction agent can circulate between the conveying device (4) and the reaction agent container (1) in such a way that, in particular when the metering device is closed, freezing of the reaction agent is prevented (freeze protection 840).;

[0009] DE 10 2009 009 711 A1 relates to an exhaust gas purification device for motor vehicles in which a fluid reducing agent is used for purifying the exhaust gas. The exhaust gas purification device for motor vehicles has a tank (1) for a fluid reducing agent (2), a nozzle (3) opening into the exhaust gas stream (4) of the vehicle for injecting the reducing agent (2) into the exhaust gas stream (4), and a pump (6; 6') for pumping the reducing agent (2) via a fluid connection from the tank (1) to the nozzle (3). According to one aspect, the exhaust gas purification device has at least one flow meter (7) for the reducing agent (2) which is arranged in the fluid connection between the tank (1) and the nozzle (3).According to another aspect, the nozzle (3) is a controlled openable and closeable nozzle 3*), which is connected via the fluid connection to the tank (1) and further to a control unit (10), and furthermore a pressure change unit (60) is provided in the fluid connection between the tank (1) and the nozzle (3) and connected to the control unit (10), which is designed to change the injection pressure of the reducing agent (2) injected via the nozzle (3) into the exhaust gas stream (4) depending on a control signal received from the control unit (10).

[0010] This problem is solved by a method for operating a conveying and dosing system as defined in claim 1. Preferred embodiments of this method, as well as a corresponding computer program and a corresponding computer program product, are defined in the further claims. Disclosure of the invention Advantages of the invention

[0011] The method according to the invention is based on a conveying and metering system designed to convey a liquid medium from a tank and to meter the medium via a pressure line by means of at least one metering unit. The system comprises at least one conveying pump and, in a separate return path, at least one device for returning the medium, in particular a return pump and / or a switching valve in the return line. The liquid medium can thus be drawn back from the pressure-side area of ​​the conveying system into the tank, for example, to remove the liquid medium from the pressure-side area and the metering unit after a suitably equipped vehicle has been parked. This prevents damage to the components caused by the pressure of freezing at low temperatures.To prevent damage to components, particularly in the return channel and its components, caused by the high temperatures of the returned medium, the invention provides for flushing the return path after and / or during the return of the medium. This prevents or significantly reduces the duration of the warm or hot medium remaining in the return channel. Consequently, the components and parts in the return line and in the tank unit, or at the interface between the conveying device and the tank—for example, the corresponding seals and other components—are exposed to the warm or hot medium only for a very short time. This reduces the stress on the components due to temperature exposure and increases their service life. The method according to the invention thus serves to cool the components and parts in the return path.The method according to the invention also serves to provide defined input variables for model calculations that work with temperature values, as will be explained in more detail below.

[0012] The return path is flushed with the metering valve closed, activating both the feed pump and the return system. In this circuit, cool medium is drawn from the tank by the feed pump and returned directly to the tank via the return line. This removes the warm or hot medium from the pressure-side part of the system from the return channel and its components. This prevents excessive heating and potential damage to the components and parts in the return channel. This component protection measure can reduce component aging and extend the service life of the components.

[0013] In a preferred embodiment of the method, the purging process according to the invention is used to improve the accuracy of input variables when modeling data for controlling the system. When the system is restarted, the models, in particular temperature models and indirect pressure models, operate using the ambient and tank temperatures. However, temperature information is generally unavailable when the medium has been drawn back from the pressure-side area of ​​the conveying system after the system has been shut down. The specific temperatures then present, which are generally higher temperatures in the return conveying path, are unknown and cannot be determined based on the available information.The purging process according to the invention, following backflow, replaces the warm or hot medium in the return channel with normal-temperature medium from the tank. This prevents warm or hot medium from remaining in the return channel and its components, particularly in the return pump and at the interface with the tank. Without this exchange of the medium in the return channel, undefined system states would exist, leading to inaccurate modeling of relevant parameters. The system according to the invention avoids these undefined system states by removing the hot medium from the return channel. Reliable temperature values ​​are then available in the system, which can be incorporated into the models. The method according to the invention thus represents a measure to improve the accuracy of the models and thereby achieve better system control.According to the invention, the models in the software, in particular temperature and pressure models, can be supplied with defined input variables, thereby improving the accuracy of the models. According to the invention, erroneous model calculations that could lead to incorrect system reactions are avoided by setting defined boundary conditions through the purging process.

[0014] In the purging process according to the invention, an applicable volume or, for example, an applicable number of pump strokes can be conveyed by the feed pump and returned to the tank via the return system. For this purpose, a switching valve, if present, in the return line can be switched accordingly. If a return pump is present, this return pump can be operated during the purging process, for example, in open-valve mode, i.e., at 100% and without pulses. Furthermore, the return pump can also be actively set to pumping mode by pulse-controlled operation. This actively supports the return of the medium to the tank and the purging process according to the invention.

[0015] The method according to the invention can be carried out in particular in a system that provides a return path separate from the conveying path for returning the medium to the tank. Preferably, the separate return path does not lead into the tank filter, but opens directly into the tank outside the tank filter.

[0016] Advantageously, the purging process according to the invention is carried out at ambient pressure or at pressures close to ambient pressure, i.e., at virtually no pressure. The method utilizes the fact that after the vehicle is switched off, the system is generally depressurized, so that the regular recirculation of medium from the pressure-side area, as well as the purging according to the invention for cooling, which takes place after recirculation or between individual recirculation processes, is carried out at approximately ambient pressure. Performing the purging according to the invention at approximately ambient pressure has the advantage that at ambient pressure or slight under- or overpressure, the compression ratio of the feed pump is always very good, even if there may be gas volumes present in the system that would make pressure build-up difficult.

[0017] It can be advantageous to activate the actuators in the pumping system, in particular the feed pump and / or the return pump or the switching valve in the return line, at staggered intervals in order to set pressure conditions that optimize the delivery of the medium and thus the flushing process. In this context, the feed pump and / or the device for returning the medium can also be activated in multiple stages and / or temporarily deactivated. This allows the flushing process according to the invention to be adapted to various conditions and adjusted to different pressure conditions. This variant of the process can be carried out depending on the detected operating conditions.

[0018] According to the invention, the return of the medium after the system is shut down and the flushing of the return path are carried out alternately. After a certain volume of medium has been returned, a short flush is performed for cooling, after which the return process continues. With this design, the time that the components and parts of the return path are exposed to the hot, returned medium can be further minimized, thereby further reducing the temperature load.

[0019] The method according to the invention can, in principle, be carried out after or during all back-suction processes, such as those that occur after each time the vehicle is switched off. By specifying suitable release conditions, the number of purging processes according to the invention can be reduced or optimized for specific applications. For example, the execution of the purging process according to the invention can be made dependent on exceeding or falling below predefinable temperature thresholds, which relate to the measured and / or modeled temperature upstream and / or downstream of the catalyst and / or the dosing unit and / or the environment and / or the tank. For instance, it may not be advantageous to carry out the purging process according to the invention if the tank temperature, i.e., the temperature in the reducing agent tank, is relatively high, since the cooling effect is comparatively small in this case.Other release conditions can be specified for each application.

[0020] The invention further comprises a computer program that executes all steps of the described method when run on a computer or control unit. The invention also includes a computer program product with program code stored on a machine-readable medium for carrying out the method according to the invention when the program is run on a computer or control unit. Implementing the method according to the invention as a computer program has the advantage that this program can readily be used in existing vehicles, thus enabling the use of the cooling of the return path in the pump system according to the invention.

[0021] Further features and advantages of the invention will become apparent from the following description of exemplary embodiments in conjunction with the drawings. The individual features can be implemented individually or in combination with one another. Brief description of the drawings

[0022] The drawings show: Fig. 1 a schematic representation of the components of a current system for the conveying and dosing of a liquid medium; Fig. 2 a hydraulic circuit diagram of a system with a return pump and Fig. 3 a hydraulic circuit diagram of a system with a switching valve for the return channel. Description of exemplary implementations

[0023] The in Fig. The conveying and metering system shown in Figure 1 for the reducing agent of an SCR catalyst system serves as an exemplary system suitable for carrying out the process according to the invention. The invention is not limited to such a system. Rather, the purging and cooling process according to the invention can also be used for other conveying and metering systems that have a return path. For example, pump systems that include a return line with a switching valve instead of a return pump are also suitable. The pump system of the conveying and metering system shown in Figure 1 is described in Figure 1. Fig. The assembly comprises a delivery module 1 and a return module 2. Delivery module 1 includes the actual delivery pump 10, which is designed as a reciprocating piston pump 10 with a solenoid 11, spring 12, diaphragm 13, and piston 14. Delivery module 1 also contains an intake valve 15 and an outlet valve 16. A return pump 20 within return module 2 is designed in a similar manner. This module also contains an intake valve 21 and an outlet valve 22.

[0024] The liquid medium is pumped from tank 3 into pressure line 4 by means of pumping module 1, in order to be metered into the exhaust gas stream (not shown) via metering module 7, which includes a metering valve 71 and an upstream strainer 72. The medium is drawn back from the pressure-side section of the pump system by activating the return pump module 2, specifically by activating the return pump 20. This return can be achieved by actively operating the return pump 20 with pulsed control. Alternatively, the return pump 20 can also be set to open valve operation.

[0025] The method according to the invention is not applicable to pumps with the in Fig. The method according to the invention is limited to the solenoid drive shown in Figure 1. It can also be used in pump systems with other pump drives (e.g., rotary motor, stepper motor).

[0026] Fig. Figure 2 shows a general hydraulic circuit diagram for a conveying and metering system for which the flushing method according to the invention can be used to cool the return conveying path. This hydraulic circuit diagram essentially corresponds to the system described in Figure 2. Fig. Figure 1 shows that other pump drives can be implemented instead of the solenoid drive. The corresponding elements of the system are identified with the same reference symbols as in Figure 1. Fig. 1. The return pump 20 is equipped with a pump. The pumping action of the return pump 20 allows the medium to be removed from the metering valve 71 and / or the pressure line 4, particularly after the system has been switched off. This prevents damage to sensitive components in the system caused by the ice pressure from the frozen reducing agent at low temperatures.

[0027] Fig. Figure 3 shows a hydraulic circuit diagram for another conveying and dosing system in which the flushing method according to the invention can also be advantageously used. In contrast to the one in Fig. In the system shown in Figure 2, this system has a switching valve 200 in the return channel instead of a return pump. In this system, the return channel or return path can be opened, allowing the medium to be pushed back into tank 3. However, it is not possible to actively pump the medium in the return path.

[0028] The purging process according to the invention is carried out after or during the backflow of medium from the pressure-side area of ​​the system, including the metering module, in order to cool the return channel. The purging process according to the invention for cooling can be carried out after the medium has been backflowed or even during the backflow process. In the latter case, the purging process according to the invention for cooling is carried out alternately with the backflow process, during which the metering valve is open. For the purging process according to the invention, the metering valve is closed or is closed at the start of the purging process. The purging process is therefore independent of the physical boundary conditions on the exhaust side. The conditions on the exhaust side may be relevant for enabling the process. The physical boundary conditions on the exhaust side have no influence on the process itself, i.e., the cooling process.

[0029] After the metering valve 71 or the metering module 7 is closed, the feed pump 10 is activated for the purging process according to the invention, and the device for returning the medium, in particular the return pump 20 or the switching valve 200 in the return path, is activated or opened. The return pump 20 can be controlled at an applicable frequency, so that the pump function is active. Alternatively, the return pump 20 can also be controlled without a pulse, so that its valve function is active, meaning that the return path is completely open. The feed pump 10 is controlled at an applicable frequency, so that liquid medium is pumped from the tank 3. Since the metering unit 7 is closed, the medium is directed from the tank 3 via the feed path and back again via the return path into the tank 3.In this way, the warm or hot medium from the back-suction process is replaced with normal-temperature medium from the tank. The purging process according to the invention is generally carried out without pressure, whereby the regular back-suction of medium from the pressure-side area of ​​the pump system is also carried out without pressure, i.e., after pressure relief of the system.

[0030] As shown in the figures, a return path separate from the conveying path to tank 3 is preferably provided for the return of the medium.

[0031] The activation of the actuators, in particular the feed pump 10 and the return pump 20 or the corresponding switching valve 200 in the return line, can be staggered. For example, the return pump 20 or the switching valve 200 in the return line can be activated first, and the feed pump 10 can be switched on after a delay. The activation of the actuators can also be changed in multiple stages during the flushing process, for example, depending on the detected operating conditions. For example, the return pump 20 can initially be fully activated to actuate its valve function. After a defined period, the return pump 20 can then be operated intermittently at a defined frequency, so that the medium is actively pumped back through the return path into tank 3.

[0032] The purging process according to the invention can be terminated normally, depending on the application, when the desired purging volume has been reached or a specific applicable number of pump strokes have been performed. Furthermore, an applicable time can be specified that must be exceeded before the purging process is terminated. Additional conditions can be specified for specific applications. Depending on the application, the purging process can also be terminated in the event of a fault. For example, the purging process can be terminated if the actuator monitoring detects a fault, such as excessive current, a short circuit, or generally an abnormal current signal. The purging process according to the invention can also be terminated upon detection of a fault in the sensor monitoring, in the event of an impermissible pressure build-up, particularly after exceeding an applicable pressure threshold, or under other application-specific conditions.

[0033] The purging method according to the invention for cooling the components and parts in the return path can, in principle, be used after or during each return suction process, for example, after each time the vehicle is parked, when the pressure-side area and / or the metering valve is routinely emptied. Suitable release conditions can also be provided to reduce or optimize the number of cooling processes according to the invention for specific applications. Possible release criteria could include, for example: - the backflow is correctly completed or correctly interrupted; - There is no fault that is interfering with the relevant actuator / sensor system; - the temperature upstream of the catalyst is above an applicable value; - the temperature downstream of the catalyst is above an applicable value; - the coil temperature of the metering valve is above an applicable value; - the temperature at the valve tip of the metering valve is above an applicable value; - the ambient temperature is below an applicable value; - the temperature of the medium tank, especially the reducing agent tank, is below an applicable value.

[0034] These specifications ensure that the purging process according to the invention is only carried out if it achieves effective cooling of the components and parts of the return path. For example, the purging process according to the invention may not result in the desired cooling of the return path if the medium in the tank is too warm. Furthermore, carrying out the cooling process according to the invention may not be effective if the returned medium does not have a high temperature. Additional conditions for the initialization or release of the purging process according to the invention can be specified for specific applications, for example, with regard to pressure line length and pressure line volume, or other conditions. The parameters required for release can be measured or derived from model calculations.

Claims

[1] Method for operating a conveying and metering system, which is designed for conveying a liquid medium from a tank (3) and for metering the medium via a pressure line (4) by means of at least one metering unit (7), wherein the system comprises at least one conveying pump (10) and at least one device for returning the medium, in particular a return pump (20) and / or a switching valve (200) for a return flow, wherein after the system is switched off, a return of medium from the pressure-side part of the system is provided, characterized by , that after and / or during the return of medium, the return path is flushed with the dosing unit (7) closed by activating the feed pump (10) and by activating the device for returning the medium, wherein the return of medium after the system is switched off and the flushing of the return path are carried out alternately. [2] Method according to claim 1, characterized by that the flushing is carried out to cool components and / or parts of the return conveying path. [3] Method according to claim 1 or claim 2, characterized by that the flushing is carried out to improve the accuracy of input variables when modeling data for controlling the system. [4] Method according to any one of the preceding claims, characterized by that the flushing of the return path is carried out at ambient pressure or pressures close to ambient pressure. [5] Method according to any one of the preceding claims, characterized by , that the feed pump (10) and / or the device for returning the medium are activated in multiple stages and / or temporarily deactivated. [6] Method according to any one of the preceding claims, characterized by, that the execution of the purging of the return path depends on predefinable release conditions, in particular on exceeding or falling below temperature thresholds relating to the measured and / or modeled temperature upstream and / or downstream of a catalyst and / or the dosing unit (7) and / or the environment and / or the tank (3). [7] Computer program that performs all the steps of a method according to any one of claims 1 to 6 when executed on a computing device or a control device. [8] Computer program product comprising program code stored on a machine-readable medium for carrying out a method according to any one of claims 1 to 6 when the program is executed on a computing device or a control device.

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