DE102012212570A1 - Method of operating conveying and dosing system of liquid medium, involves performing rinse within conveying and dosing system during heating of conveying and dosing system by heating device according to thawing out mediums in system - Google Patents

Abstract

The mediums are conveyed from tank over an activation of feed pump with closed metering unit and the device for the back promotion of the mediums is activated. A rinse is made within the conveying and dosing system during heating of the conveying and dosing system by heating device according to thawing out mediums in the system. An independent claim is included for computer program product for operating conveying and dosing system.

Description

The present invention relates to a method for operating a delivery and metering system, which is provided 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 a conveying path with at least one feed pump and a return feed path with at least one device for returning the medium. Furthermore, at least one device is provided for heating the delivery and metering system. Moreover, the invention relates to a computer program and a computer program product with program code, which are suitable for carrying out the method.

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 (NOx) 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, which is admixed to the exhaust gas. For the supply of ammonia, an aqueous urea solution is usually used, which is injected into the exhaust line upstream of the SCR catalyst by means of a metering device.

The urea solution is usually kept in a urea solution tank in the motor vehicle. To promote the urea solution, a delivery and metering system is generally provided which, in addition to the urea solution tank, comprises a delivery unit, a pressure line, a metering unit, the required sensors and an electronic control unit. Furthermore, one or more heating device (s) are provided, which can heat the delivery and metering system at low ambient temperatures and possibly thaw the medium / can to enable the system in metering readiness. For example, three heating circuits may be provided, in particular a tank heater, a heating of the pressure line and a heating of the pump system. The heating of the pump system can be realized, for example, via the existing coils of the installed pump (s). In the following, the entire delivery and metering system, which in particular includes the tank, the pump (s), valves, lines, the metering device, the sensor system and a control unit, is referred to as a system. The pump system in the narrower sense mainly comprises the pump (s), possibly pulsation dampers, as well as lines and valves.

As an essential component of the delivery and metering system, a delivery pump is generally provided which conveys the desired and required amount of urea solution from the tank and feeds in a system pressure range in the pressure line. About the metering unit, which may include one or more metering valves, the urea solution is sprayed as needed in the exhaust system.

In order to avoid damage to the sensitive components of this system by ice pressure at low temperatures, it is generally provided that after switching off the internal combustion engine or the motor vehicle, the urea solution is sucked from the metering unit back into the tank. For this purpose, for example, the feed pump may be equipped with a switching unit, for example a 4/2-way valve. In other systems, a separate return channel is provided with switching valve. Newer systems may have a separate return channel with a separate return pump that allows the return of medium from the metering unit and possibly from the pressure line.

If the system has to be heated at low ambient temperatures and the medium in the system is partially or completely thawed, this process, which is also referred to as the "defrost" process, can result in undefined starting conditions and possibly locally very different states of the medium and of the components and Components of the system are present. For example, it can occur that the medium is not uniformly and / or in part not completely thawed, so that inaccuracies in the dosage can occur. Furthermore, due to the thawing process, gas or vapor inclusions can occur in the pump system, which impair the functioning of the system. In addition, the uneven heating within the delivery and metering system can cause different input variables for temperature and pressure models are inaccurate and thus can not or only partially be used for another system control. Erroneous model calculations can lead to incorrect system reactions and may severely limit the performance of the system.

The invention is based on the object to improve the method for operating a conveying and metering system and in particular after and / or during heating of the delivery and metering system, especially after a partial or complete thawing of medium in the system, the operational readiness with defined conditions and in addition to solve the problem after and / or during one Heating the system, and especially after thawing medium in the system, will not provide reliable values as inputs to various model calculations.

This object is achieved by a method for operating a conveying and metering system, as is apparent from the claim 1. Preferred embodiments of this method and a corresponding computer program and a corresponding computer program product result from the further claims.

Disclosure of the invention

Advantages of the invention

The inventive method is based on a delivery and metering system, which is provided 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. For example, this is the delivery and metering system for liquid urea solution, which is sprayed into the exhaust tract upstream of an SCR catalyst. The system comprises at least one feed pump and in a separate return path at least one means for the return of the medium, in particular a return pump and / or a switching valve in the return. The medium can thus be sucked back into the tank from the pressure-side region of the delivery system in order to be able to remove the liquid medium from the pressure-side region and the dosing unit, for example, after parking a suitably equipped motor vehicle. As a result, damage to the components at low temperatures can be avoided by the ice pressure caused by frozen medium. The conveying and metering system also has one or more heating devices for heating the conveying and metering system. Heating devices are required in order to thaw the optionally frozen medium in the conveying and dosing system at low ambient temperatures, so that the system can be set to dosing standby. For example, a tank heater, a pressure line heater and a heater of the pump system may be provided. According to the invention, it is provided that after and / or during the heating of the delivery and metering system and in particular after thawing of medium in the system, especially after thawing of medium in the tank and in the / the pump (s) by actuation of the corresponding heaters, a rinse is made. For this purpose, liquid medium is conveyed from the tank by means of the feed pump, wherein the metering unit or the metering valve is closed. Furthermore, the means for returning the medium is activated, so that the return path is opened. In the case that a switching valve is provided for the return, the switching valve is opened. In the event that a return pump is present in the system, the return pump can be set to open valve operation or pumping operation. In this cycle thus formed liquid medium is conveyed from the tank via the feed pump and returned directly via the return to the tank. The medium, which was in the pump system during thawing or heating, is displaced and conveyed back into the tank via the return channel. In the course of this rinsing process uniformly tempered medium is distributed from the tank in the pump system.

The rinsing process according to the invention can take place after the thawing of medium and / or during the heating of the system, as soon as sufficient liquid medium is available to carry out the rinsing process. Sufficient liquid medium will usually be present when the heating has been carried out for a certain period of time. A sufficient period of time can be specified application-specific. For example, depending on the outside temperatures, it may be provided that the heating is continued during the rinsing, in particular also to avoid re-freezing. As a rule, heating of the pumps takes place indirectly anyway when energy is converted into heat during the activation of the pumps in the course of the flushing process according to the invention in the coils of the pumps. With a low pumping frequency of the pumps, during the available pause times (pause with respect to pump strokes), additional heating energy can be introduced via the coils by additional current supply. Also, a tank heater and / or a pressure line heater may optionally continue to operate during the flushing process according to the invention.

With particular advantage, the rinsing method according to the invention is used to ensure that the operation of the conveying and dosing system is established with defined conditions by the rinsing. Above all, possibly present gas or vapor volumes, which are caused by the thawing process, are flushed out of the system by the rinsing process according to the invention. Under certain circumstances, medium which has not completely thawed out can also be flushed out, so that defined and uniform conditions of the medium are provided in the system. Furthermore, by the distribution of uniformly tempered medium from the tank in the conveying and metering system defined conditions can be made in particular with regard to the temperature of the various components and components of the system. This may be particularly important in systems without a pressure sensor, in which a pressure interpretation, for example, from the current signal of the feed pump. For this an estimate of the temperature of the pump diaphragm is needed. Since the state of the medium after thawing is largely unknown, an estimation of the membrane temperature without the rinsing method according to the invention (ie without an exchange of medium) can be erroneous and thus lead to a wrong pressure modeling. The rinsing process according to the invention avoids this uneven temperature distribution. The membrane temperature can thus be estimated much more accurately, so that the pressure interpretation can be done in a reliable manner from the current signal of the pump. Also for other models in the software, especially for different temperature models or printing models, input parameters defined by the purge process of the present invention may be provided to improve the modeling of values in accuracy or to avoid erroneous model computations that could lead to false system responses. The advantages of the rinsing process according to the invention thus lie in the fact that after or during a heating of the system and in particular after a partial or complete thawing of medium within the pump system, the temperatures are adjusted to the tank temperature over the entire system. Possible inclusions of air, steam or gas in the system are flushed out. Thus, for example, a possible formation of steam, which may occur due to local overheating during thawing of the medium during heating, or any residual air which may still be present, is flushed out of the pump system by the flushing method according to the invention and conveyed into the tank. Thus, the method according to the invention allows the various states of the system, in particular with regard to the temperature control of the medium, with regard to the state of aggregation of the medium and with regard to the pump membrane temperatures, to lie within an assessable or limited range.

The flushing method according to the invention makes it possible to produce a defined system state with regard to the various components and parameters of the pump system by means of the temperature control, in particular with regard to the temperature as well as rigidity of the pump diaphragms and the like. This plays a role especially for the feed pump and the optionally present return pump, since the temperature of the pump diaphragms is decisive for their function. Also, for example, a defined temperature of an optionally existing Pulsationsdämpfers is advantageous for its function. Finally, the models in the software, in particular temperature models or printing models, can be supplied with defined input variables by the rinsing method according to the invention. In this way, defined boundary conditions can be set, and the accuracy of the models is improved.

The rinsing method according to the invention can be carried out after a defrost phase, ie after the heating of the system for thawing the medium, in particular after activation of the tank heating and / or the pump system heating, in order to achieve system optimization. The rinsing process can already be carried out already if sufficient liquid medium is available through the thawing process. During the flushing process, the heating can be continued. As a result, a complete thawing of the medium in the system can optionally be achieved. Furthermore, a re-freezing of the medium can be avoided at correspondingly low outside temperatures.

To carry out the rinsing process according to the invention, for example, an administrable volume can be conveyed by the delivery pump and returned to the tank via the return pump or the switching valve in the return. The flushing process can be carried out, for example, with an applicable number of pump strokes of the feed pump. If a switching valve is present in the return, this switching valve can be switched according to the rinse cycle. If a return pump is present, this return pump during the purging process, for example, in open valve operation, i. at 100% and not clocked, are controlled. Furthermore, the return pump can also be actively set to pump mode by being controlled clocked. As a result, the return conveyance into the tank or the flushing process according to the invention can be actively supported.

The inventive method is provided for a system that provides for the return of the medium into the tank a separate from the conveying path return. Preferably, the separate return path does not lead into the tank filter, but flows outside the tank filter directly into the tank. In this way, it can be avoided that steam or gas volumes, which are conducted into the tank in the course of the rinsing process according to the invention, remain in the tank filter and could be sucked back into the conveying system.

Advantageously, the rinsing method according to the invention is carried out at ambient pressure or at pressures close to the ambient pressure, that is to say almost without pressure. Here, the inventive method uses that the defrost process itself in the pressure normally takes place or approximately at ambient pressure. The rinsing process can therefore be carried out immediately afterwards or after a certain period of time in parallel, without any further relief of the system having to be carried out. The implementation of the rinsing process according to the invention at about ambient pressure has the advantage that at ambient pressure or small under or overpressures, the compression ratio of the feed pump is in any case sufficiently good to promote and eliminate possible gas volumes from the element space of the pump can.

It may be advantageous to actuate the actuators in the pump system, that is to say in particular the feed pump and / or the return pump, in such a way that a low negative pressure or a slight overpressure arises on the pressure side of the feed pump. Depending on the application, this can speed up and optimize the rinsing process. Furthermore, it may be advantageous to activate or open the delivery pump and the device for returning the medium, ie in particular the return pump or the switching valve in the return, with a time delay. For example, the feed pump can be activated delayed in time. Also, this pressure ratios can be adjusted, which optimize the promotion of medium from the tank and thus the rinse. In this context, the feed pump and / or the device for returning the medium can be activated in multiple stages and / or temporarily deactivated. Thus, the rinsing method according to the invention can be adapted to different conditions and adjusted to different pressure conditions. This variant of the method can be carried out, for example, depending on the detected operating conditions and / or application-specific applied.

The rinsing method according to the invention can, in principle, be carried out after and / or with a time delay during all defrost operations. By specifying suitable release conditions, the number of rinsing operations can be reduced or optimized application-specific, whereby conservation of the components can be achieved. Therefore, it is preferably provided that the release conditions and / or the termination conditions and also optionally the operating parameters for the flushing are applied application-specific.

In a further embodiment of the method according to the invention, it is provided that a successful and completed flushing is checked by the recirculation path is closed and is observed based on a pressure build-up in a pumping operation of the feed pump, ie with active feed pump, whether an expected pressure build-up takes place. If no even distribution of thawed and uniformly tempered medium has taken place in the pump system and, for example, gas volumes are still present in a significant amount in the system, the expected pressure build-up can not take place. In this case, the rinsing process can be continued or an error may be set.

The invention further includes a computer program that performs all the steps of the described method when executed on a computing device or controller. Furthermore, the invention comprises 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 executed on a computing device or a control device. The implementation of the method according to the invention as a computer program has the advantage that this program can also be used without problems in existing vehicles so as to be able to utilize the advantages of the flushing method according to the invention in connection with defrost processes in the conveying and metering system.

Further features and advantages of the invention will become apparent from the following description of exemplary embodiments in conjunction with the drawings. In this case, the individual features can be implemented individually or in combination with each other.

Brief description of the drawings

In the drawings show:

1 a schematic representation of the components of a current system for the delivery and metering of a liquid medium;

2 a hydraulic circuit diagram of a system with return pump from the prior art and

3 a hydraulic circuit diagram of a system with switching valve for the return channel from the prior art.

Description of exemplary embodiments

This in 1 shown conveying and metering system for the reducing agent of an SCR catalyst system serves as an exemplary system that is suitable for carrying out the method according to the invention. The invention is not limited to such a system. Rather, that can Rinsing methods according to the invention are also used for other conveying and metering systems, which have a separate recirculation path. For example, pump systems are suitable, which have a return valve with switching valve instead of a return pump. The pump system of the delivery and metering system 1 includes a conveyor module 1 and a return module 2 , The conveyor module 1 this includes the actual feed pump 10 acting as a reciprocating pump 10 with lifting magnet 11 , Feather 12 , Membrane 13 and reciprocating pistons 14 is designed. Furthermore, a suction valve 15 and an exhaust valve 16 in the conveyor module 1 available. A return pump 20 within the return module 2 is designed in principle in a corresponding manner. In this module are also an inlet valve 21 and an exhaust valve 22 available.

In the regular dosing operation, the liquid medium from the tank 3 by means of the conveyor module 1 in the pressure line 4 promoted to the dosing module 7 that is a metering valve 71 and an upstream sieve 72 includes, to be metered into the exhaust line (not shown). A regular sucking back of the medium from the pressure-side region of the pump system after stopping the system takes place via an activation of the suck-back module 2 , ie in particular via an activation of the return pump 20 , The return flow can be achieved by active pumping of the return pump 20 be made with clocked control. On the other hand, it is also possible, the return pump 20 to open valve operation.

The inventive method is not on pumps with the in 1 limited shown lifting magnet drive. The inventive method can also be used in pump systems with other pump drives (eg rotary motor, stepper motor).

2 shows a general hydraulic circuit diagram for a conveying and metering system from the prior art, for which the flushing method according to the invention can be used. In essence, this hydraulic diagram corresponds to the system used in 1 is shown, wherein instead of the Hubmagnetenantriebs other pump drives can be realized. The corresponding elements of the system are denoted by the same reference numerals as in FIG 1 Mistake. By pumping the return pump 20 the medium can in particular after switching off the system from the metering valve 71 and / or from the pressure line 4 be removed. Thus, at low temperatures damage to the delicate components in the system can be avoided by the ice pressure caused by the frozen reductant.

3 shows a hydraulic circuit diagram for a further conveying and metering system, in which the flushing method according to the invention can also be used with advantage. Unlike the in 2 shown system, this system instead of a return pump, a switching valve 200 in the return channel. In this system, so the return channel or return path can be opened, whereby the medium in the tank 3 can be pushed back. However, it is not possible to actively pump the medium in the return path.

The rinsing process according to the invention is carried out after and / or during a defrost phase, ie after and / or during a phase of heating the conveying and dosing system and partial or complete thawing of the medium. By this rinsing process after and / or during the defrost phase, a defined system state can be established with respect to the components of the pump system. Furthermore, this uniformly tempered medium can be distributed in the pump system and possibly existing gas volumes can be removed from the pump system. For carrying out the rinsing process according to the invention, the dosing valve is closed or it is closed at the beginning of the rinsing process. The flushing process is thus independent of physical boundary conditions of the exhaust gas side. However, the exhaust side conditions may be relevant to the release of the process. The physical boundary conditions of the exhaust gas side have no influence on the process itself, ie the flushing process. After closing the dosing valve 71 (metering 7 ) or with closed metering valve 71 (metering 7 ) is for carrying out the rinsing process according to the invention, the feed pump 10 activated. The feed pump is controlled in this case in particular with an applicable frequency. The return path is opened, ie the means for returning the medium is activated. In the case of an existing switching valve 200 in the return path is the switching valve 200 open. If a return pump 20 is present, the return pump can 20 be controlled with applizierbarer frequency, so that their pumping function is active. On the other hand, the return pump 20 be driven without clocking, so that their valve function is active, ie that the return path is completely open. The opening of the return path and the control of the pump can be done simultaneously or offset in time. By the pumping operation of the feed pump is already thawed medium from the tank 3 promoted. Because the dosing unit 7 is closed, the medium is from the tank 3 over the conveying path and back again via the return path into the tank 3 directed. In this way, thawed and uniformly tempered medium is distributed from the tank in the pumping system, displacing the medium thawed during the defrosting process from the pumping system. The flushing process according to the invention can be carried out without pressure. Since usually the defrost process is already without pressure, therefore, the subsequent or accompanying rinsing process can be made without further pressure relief of the system. Depending on the application, however, can also by appropriate control of the actuators in the system, a small negative pressure or a small overpressure on the pressure side of the feed pump 10 be prepared to optionally optimize the inventive flushing process and / or to accelerate.

The activation of the actuators, so in particular the feed pump 10 and the return pump 20 or the corresponding switching valve 200 in the return, can be staggered by, for example, first the return pump 20 or the switching valve 200 is controlled in the return and after a delay time, the feed pump 10 is turned on. The actuation of the actuators can also be changed in several stages during the rinsing process, for example as a function of the detected operating conditions. For example, the return pump 20 initially fully activated to the valve function of the return pump 20 to press. After an applicable time, the return pump 20 clocked to be operated with applicable frequency, so that the medium is active through the return path into the tank 3 is pumped back.

Depending on the application, the rinsing method according to the invention can be terminated regularly when the desired rinsing volume has been reached or a certain number of pump strokes has been applied. Furthermore, an applicable time can be specified, which must be exceeded before the rinsing process is terminated. Other conditions can be specified application-specific. Depending on the application, the rinsing process can also be terminated in the event of an error. For example, the flushing process may be terminated when the actuator monitoring detects an error, such as too high a current, a short circuit or generally a current signal that is out of order. Also in the detection of a fault in the sensor monitoring or in an impermissible pressure build-up, in particular after exceeding an applicable pressure threshold, or in other application-specific conditions, the flushing process according to the invention can be terminated.

• – der aktuelle Defrost-Zyklus ist korrekt, d.h. ohne Fehler beendet worden;
• – es liegt kein Fehler vor, der die zuständige Aktorik/Sensorik sperrt.

The flushing process according to the invention can in principle be carried out after all defrosting operations. The rinsing process can also be carried out as an accompaniment to all defrost processes, provided that sufficient liquid medium already exists in the system. Advantageously, the number of rinses performed by appropriate release conditions after or during the defrost phases can be application-specific reduced or optimized, so that a protection of the actuators in the pump system and optionally also a time-optimized design are possible. Possible criteria for the release can be, for example:

• - the current defrost cycle is correct, ie ended without error;
• - There is no error blocking the responsible actuators / sensors.

Other conditions for the release of the rinsing method according to the invention can be specified and adapted application-specific.

Claims (11)

Method for operating a delivery and metering system for delivering a liquid medium from a tank ( 3 ) and for metering the medium via a pressure line ( 4 ) by means of at least one dosing unit ( 7 ), the system having a conveying path with at least one delivery pump ( 10 ) and a return path with at least one device for returning the medium, in particular a return pump ( 20 ) and / or a switching valve for a return ( 200 ), wherein at least one heating device is provided for heating the conveying and metering system, characterized in that after and / or during heating of the conveying and metering system by at least one heating device, in particular after thawing of medium in the conveying and metering system, a purge is carried out within the delivery and metering system by removing medium from the tank ( 3 ) via an activation of the feed pump ( 10 ) with closed dosing unit ( 7 ) and the institution for the return of the medium ( 20 ; 200 ) is activated. A method according to claim 1, characterized in that the flushing is carried out for producing the operational readiness of the conveying and metering system. A method according to claim 1 or claim 2, characterized in that the purging to improve the accuracy of input variables in the modeling of data for controlling the system takes place. Method according to one of the preceding claims, characterized in that the flushing is carried out at ambient pressure or pressures near the ambient pressure. Method according to one of the preceding claims, characterized in that the device for returning the medium to a return pump ( 20 ) and that the return pump ( 20 ) is controlled such that a low negative pressure or a slight overpressure on the pressure side of the feed pump ( 10 ) arises. Method according to one of the preceding claims, characterized in that the feed pump ( 10 ) and the facility for the return of the medium ( 20 ; 200 ) are activated offset in time, wherein preferably the feed pump ( 10 ) is activated with a time delay. Method according to one of the preceding claims, characterized in that the feed pump ( 10 ) and / or the facility for the return of the medium ( 20 ; 200 ) are activated in several stages and / or temporarily deactivated. Method according to one of the preceding claims, characterized in that the operating parameters and / or the release conditions and / or the termination conditions for the flushing are applied application-specific. Method according to one of the preceding claims, characterized in that a successful flushing is checked by the means for returning the medium ( 20 ; 200 ) is closed and a pressure build-up with active feed pump ( 10 ) is monitored. A computer program that performs all the steps of a method according to any one of claims 1 to 9 when executed 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 1 to 9, when the program is executed on a computing device or a control device.

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