Method for operating a control unit, control unit program, control unit program product and device for carrying out the method

Abstract

Method for operating a control unit (26) which controls a reagent dosing system (30) arranged in a motor vehicle, comprising - Starting the control unit (26) after a main power supply voltage (KI-30) occurs, regardless of a start-up signal (KI-15) from the motor vehicle, - Querying the fill level of the reagent dosing system (30) stored in a memory (32) of the control unit (26) and - Emptying the reagent dosing system (30) if the fill level indicates that the emptying of the reagent dosing system (30) was not completed when the control unit (26) was last switched off due to the loss of the main power supply voltage (KI-30).

Description

[0001] The present invention relates to a method for operating a control unit which controls a reagent dosing system arranged in a motor vehicle.

[0002] Additionally, the present invention relates to a specially designed control unit for carrying out the method.

[0003] Furthermore, the present invention relates to a control unit program that executes all steps of the method according to the invention when it runs in a control unit.

[0004] Finally, the present invention relates to a control unit program product with program code stored on a machine-readable carrier for carrying out the method according to the invention when the program runs in a control unit. State of the art

[0005] To comply with increasingly stringent emissions regulations, it is necessary to reduce nitrogen oxides (NOx) in the exhaust gas of internal combustion engines, particularly diesel engines. One known method for this is to install a selective catalytic reduction (SCR) catalyst in the exhaust manifold of internal combustion engines. This catalyst reduces the nitrogen oxides contained in the exhaust gas to nitrogen in the presence of a reagent / reducing agent. This significantly reduces the proportion of nitrogen oxides in the exhaust gas. Ammonia (NH3) can be used for this reaction, which is added to the exhaust gas upstream of the SCR catalyst. Therefore, NH3 or, preferably, NH3-releasing reagents are used as the reagent. Typically, an aqueous urea solution (urea-water solution) is used, which is injected into the exhaust gas channel upstream of the SCR catalyst.Ammonia, which acts as a reducing agent, is formed from the urea-water solution through hydrolysis. A 32.5% aqueous urea-water solution is sold under the brand name AdBlue. ® commercially available.

[0006] Modern control units that operate hydraulic components using aqueous solutions as their operating medium often have to ensure that the system is partially or completely drained during the shutdown phase (control unit overrun) of the hydraulic system, as the hydraulic components frequently cannot be designed to withstand freezing pressure. This is precisely the process used in SCR catalytic converter systems that use AdBlue. ®The reagent used has a freezing point of approximately -11 °C. In a motor vehicle, the reagent dosing system is emptied during a control unit overrun with the ignition switched off, in order to protect components such as the pump, connections, valves, and the like from damage caused by freezing pressure.

[0007] Whether the reagent dosing system is filled or empty is stored in the control unit, for example in an EEPROM, so that the information is not lost even in the event of short-term voltage interruptions (µ-cuts) or voltage pulses, such as Type 1 ISO 7637 pulses on the main power supply corresponding to the voltage at terminal 30, which trigger a restart of the control unit. In this way, voltage interruptions that cause a reset of the control unit during the driving cycle of a motor vehicle, i.e.,From the state of commissioning voltage "on" to commissioning voltage "off", the voltage or no voltage at the so-called terminal 15 of the ignition switch must be handled correctly, since the information about the fill level of the reagent dosing system is read back from the memory when the software is restarted and thus the "Empty" function can be called up in the control unit after-run.

[0008] This method, however, has a weakness that becomes apparent when the voltage interruption or pulse, combined with a reset of the control unit, occurs after the start of the control unit's overrun. The control unit's overrun is typically initiated by changing the commissioning voltage or the ignition signal at terminal 15 from "on" to "off". If the control unit performs a reset during the overrun, the subsequent startup of the control unit occurs with the commissioning voltage at terminal 15 set to "off". In this case, at least parts of the control unit's software are not started and wait to start until the commissioning voltage at terminal 15 changes from "off" to "on".The consequence of this behavior is that the control unit's after-run, interrupted by the reset, is not resumed, potentially leading to a full reagent dosing system being shut down. At sufficiently low ambient temperatures and with a sufficiently long subsequent period of vehicle inactivity, freezing of the filled reagent dosing system is to be expected. Resulting damage from frost pressure cannot be ruled out.

[0009] DE 10 2013 105 710 A1 describes a method for operating a device for conveying a liquid, in particular for dosing AdBlue. ®in SCR systems. The process involves filling and emptying the conveying line, with the fill level being detected by a pressure sensor based on a sudden pressure increase / decrease. This document focuses on the precise control of the filling and emptying process and the prevention of leaks and damage from freezing. Disclosure of the invention

[0010] The inventive method for operating, in particular for starting up, a control unit which controls a reagent dosing system arranged in a motor vehicle comprises - starting the control unit regardless of the occurrence of a commissioning voltage or a voltage at terminal 15, when a main power supply voltage or a voltage at terminal 30 of the motor vehicle occurs, - querying the fill level of the reagent dosing system stored in a memory of the control unit and - emptying the reagent dosing system if it is detected from the stored fill level that the emptying of the reagent dosing system was not completed when the control unit was last switched off due to the loss of the main supply voltage.

[0011] The start-up voltage at terminal 15 corresponds to the presence of voltage at terminal 15 and signals a request to start the vehicle. Typically, when the ignition key is turned to the start position, a vehicle electrical system voltage appears at terminal 15, whereupon various functions in switching devices are initiated, which are supplied with electrical energy from the vehicle's electrical system. In addition to the start-up voltage, a main power supply voltage also occurs in the vehicle electrical system, particularly in commercial vehicles. This voltage appears at terminal 30, which is directly connected to the vehicle's battery. The main power supply voltage is usually switched on by a main relay control, which is present especially in commercial vehicles whose electrical system can be completely disconnected from the battery by means of the main relay control.

[0012] The invention assumes that the control unit, which determines the dosage of a reagent in a reagent dosing system installed in a motor vehicle, receives both the start-up voltage and the main power supply voltage. The main power supply voltage enables a control unit overrun, which is thus possible even after the ignition key has been turned to switch off the internal combustion engine, i.e., when the start-up voltage has already been switched off.

[0013] Voltage dips in the main power supply cause the control unit to reset after the dip has subsided. Intentionally switching off the main power supply prematurely will only cause the control unit to reset once the main power supply voltage is restored at terminal 30.

[0014] A problematic situation arises particularly when the control unit's post-run cycle for emptying the reagent dosing system is not completed, and a voltage drop at terminal 30 or a complete loss and subsequent reappearance of the main power supply voltage at terminal 30 each leads to a reset of the control unit. In these cases, complete emptying of the reagent dosing system is not guaranteed, so freezing of the reagent cannot be ruled out.

[0015] The inventive method for operating the control unit causes the control unit to perform a software reset independently of the commissioning voltage at terminal 15 as soon as the main power supply voltage is available at terminal 30, whereby the fill level determined during the emptying of the reagent dosing system in the last control unit after-run and constantly updated and stored in a memory of the control unit is queried.

[0016] The information about the stored fill level is used to decide whether the control unit's post-run was aborted in the "filled" state or not. Depending on the outcome of this decision, the aborted control unit post-run is resumed, and the reagent dosing system is emptied again. The control unit can then be shut down. Normally, the control unit is restarted when the commissioning voltage is applied to terminal 15.

[0017] An advantageous embodiment provides for the acquisition of at least one measure of the temperature of the reagent dosing system. For example, the signal from an ambient air temperature sensor can be used for this purpose, the signal reflecting at least an approximate measure of the temperatures of individual components of the reagent dosing system.

[0018] The temperature measurement recorded during a reset of the control unit can be taken into account when deciding whether to empty the reagent dosing system.

[0019] A further development of this design provides that at least one temperature reading of the reagent dosing system is recorded during a control unit reset, and that the control unit permanently prevents the reagent dosing system from being activated if the recorded temperature falls below a predefined temperature threshold. This temperature threshold can be selected to prevent the reagent dosing system from being activated if a filled, switched-off reagent dosing system would start up and a temperature would be recorded at which ice damage to the hydraulic components of the reagent dosing system could no longer be ruled out. In this way, consequential damage from already damaged components can be minimized.Permanently preventing the reagent dosing system from being put into operation can be achieved, for example, by providing a locking signal which is stored in a memory of the control unit.

[0020] Further training stipulates that the activation of the reagent dosing system in the control unit is only permanently prevented if the number of instances where the temperature falls below the threshold, when the reagent dosing system is at least partially filled, exceeds a certain threshold. This threshold can be selected so that the activation of the reagent dosing system is only permanently prevented when there is a high probability of ice damage due to multiple instances where the temperature falls below the threshold, even with the reagent dosing system at least partially filled.

[0021] One design provides that every instance where the temperature falls below the threshold value, based on the measured temperature when the reagent dosing system is not completely empty, is stored in the control unit's memory. This allows critical start-up processes of the control unit ("reagent dosing system filled" or "reagent dosing system frozen") to be counted, and the number of these incidents is made available as information for investigating defective components of the reagent dosing system. This provides a basis for deciding whether the complaint is justified or should be rejected as an unjustified claim by the end customer.

[0022] The method according to the invention is carried out by a control unit that is specially prepared and configured for carrying out the method.

[0023] The method according to the invention can be executed by a control unit program if this program runs in a control unit. This makes it possible, for example, to implement the method in the control unit of a motor vehicle without having to make any structural modifications to it.

[0024] According to the invention, a control unit program product with program code, which is stored on a machine-readable medium, is also provided for carrying out this method when the program is executed in the control unit. Brief description of the drawing

[0025] An embodiment of the invention is shown in the drawing and explained in more detail in the following description. Fig. Figure 1 schematically shows a reagent dosing system of a motor vehicle, Fig. Figure 2 shows a flowchart for operating a control unit that controls the reagent dosing system and Fig. Figure 3 shows another flowchart of a process that takes place in the control unit. Exemplary embodiments of the invention

[0026] The inventive method for operating a control unit which controls a reagent dosing system can be carried out in a motor vehicle which has a known SCR catalyst system (for example, one of the DENOX systems of the applicant).

[0027] Fig. Figure 1 schematically shows components of a reagent dosing system which provides a reagent for an SCR catalyst.

[0028] In the exhaust channel 10 of an internal combustion engine 12, an SCR catalyst 14 is arranged, which selectively reduces nitrogen oxides in the exhaust gas by selective catalytic reduction (SCR). For this reaction, ammonia (NH3) is used, for example, as a reagent. Since ammonia is a toxic substance, it is obtained, for example, from the non-toxic carrier substance urea. Urea is supplied in the form of a liquid urea-water solution (AdBlue). ® ), a precursor of the reagent, is injected into the exhaust gas channel 10 upstream of the SCR catalyst 14 via a metering valve 16, for example an electromagnetic metering valve.

[0029] The urea-water solution is drawn from a tank 18 via a suction line 20. The urea-water solution is pumped by a pump 22. The urea-water solution is then conveyed under pressure through a pressure line 24 to the metering valve 16. The metering valve 16 and the pump 22 are controlled by a control unit 26.

[0030] A return pump 28, controlled by the control unit 26, is provided for drawing back the reagent from the suction line 20, the feed pump 22, the pressure line 24, and the metering valve 16. Alternatively, switching devices (not shown) may be provided so that the feed pump 22 can also transport the reagent back into the tank 18.

[0031] In addition to other signals not shown in detail, the control unit 26 receives a commissioning voltage KI-15 and a main power supply voltage KI-30.

[0032] The control unit 26 contains a level memory 32 in which the current level of the reagent dosing system 30 is constantly updated and stored.

[0033] An ambient air temperature sensor 34 is provided. The signal provided by the ambient air temperature sensor 34 is considered at least as a measure of the temperature of the components of the reagent dosing system 30.

[0034] Fig. Figure 2 shows a work cycle of the control unit 26, which begins at an initial time point 40, during which the control unit 26 is switched off and waits for the main power supply voltage KI-30 to appear at terminal 30. To start the vehicle, the driver, particularly of a commercial vehicle, first switches on the main power supply voltage KI-30 using a main switch. The appearance of the main power supply voltage KI-30 at the initial time point 40 always results in a reset of the control unit 26. At a second time point 42, the control unit 26 is started and initialization software is executed. At a third time point 44, the control unit 26 is initialized and waits for a waiting period 46 for the appearance of a commissioning voltage KI-15, which occurs at terminal 15. The commissioning voltage at terminal 15 occurs when the driver turns the vehicle's ignition key to the ready position.

[0035] With the occurrence of the commissioning signal KI-15 at a fourth time point 48, the control unit 26 commences normal dosing operation, in which the reagent for the SCR catalyst 14 is dosed. At a fifth time point 50, when the commissioning voltage KI-15 disappears, the control unit 26 terminates the dosing operation.

[0036] At this point, however, the main power supply voltage KI-30 is still present, so a control unit overrun 52 begins immediately afterwards, in which the backflow pump 28 is activated to empty the reagent dosing system 30. Simultaneously with the emptying, the reagent fill level in the reagent dosing system 30 is continuously updated in the level memory 32 of the control unit 26.

[0037] At a sixth point in time 54, when the reagent dosing system 30 is completely empty, the control unit overrun 52 is terminated. Then, at a seventh point in time 56, the main power supply voltage KI-30 is cut off by the complete shutdown of the vehicle.

[0038] If the emptying of the reagent dosing system 30 is not completed, for example due to a power interruption or a complete shutdown of the vehicle's main power supply voltage KI-30 during the control unit overrun 52, at least some of the reagent may remain in the reagent dosing system 30. At ambient temperatures below the reagent's freezing point, approximately -11°C for a urea-water solution, freezing of the reagent must be expected, and damage to components of the reagent dosing system 30 cannot be ruled out.

[0039] According to the invention, after a drop or interruption of the main power supply voltage KI-30 and after a reappearance of the main power supply voltage KI-30 during the reset of the control unit 26, the fill level of the last emptying process stored in memory 32 is read out. This allows the system to detect that the last control unit overrun 52, and thus the emptying of the reagent dosing system 30, may not have been completed.

[0040] In this case, the control unit overrun 52 continues and the reagent dosing system 30 is completely emptied. This process is recorded in the memory 32 of the control unit 26.

[0041] Fig. Figure 3 shows a flowchart, which continues to run in control unit 26.

[0042] In an initial query 60, it is checked whether an interlock signal, which can be stored in memory 32, is set. The interlock signal permanently prevents the reagent dosing system 30 from being started up if it must be assumed that ice pressure damage has already occurred.

[0043] If no locking signal is present, a second query 62 checks whether the fill level stored in memory 32 corresponds to an emptied reagent dosing system 30.

[0044] If this is not the case, a third query 64 checks whether the outside air temperature provided by the outside air temperature sensor 34 is higher than a predefined temperature threshold. This third query 64 is provided as a possible further training.

[0045] If this is the case, meaning that freezing of the reagent is not expected, the emptying of the reagent dosing system 30 is resumed in a first functional block 66, and the interrupted last control unit post-run 52 is completed. In a second functional block 68, a fill level value corresponding to an empty reagent dosing system 30 is now entered into the memory 32.

[0046] The control unit 26 then waits for the occurrence of the commissioning voltage KI-15, when the dosing operation begins.

[0047] However, if the third query 64, as provided for in a first further development, determines that a predefined temperature threshold has been undershot, the counter reading of a freezing counter is incremented by one in a third function block 70, as provided for in another further development. Subsequently, a fourth query 72 checks whether the freezing counter has a counter reading higher than a threshold for the number of instances below the threshold.

[0048] If this is not the case, the process continues with the emptying of the reagent dosing system 30 according to the first functional block 66.

[0049] However, if the fourth query 72 determines that the threshold for the number of occurrences has been exceeded, a fourth function block 74 sets the locking signal, which permanently shuts down the reagent dosing system 30. In this case, a signal is sent indicating that service is required.

Claims

[1] Method for operating a control unit (26) which controls a reagent dosing system (30) arranged in a motor vehicle, comprising - Starting the control unit (26) after a main power supply voltage (KI-30) occurs, regardless of a start-up signal (KI-15) from the motor vehicle, - Querying the fill level of the reagent dosing system (30) stored in a memory (32) of the control unit (26) and - Emptying the reagent dosing system (30) if the fill level indicates that the emptying of the reagent dosing system (30) was not completed when the control unit (26) was last switched off due to the loss of the main power supply voltage (KI-30). [2] Method according to claim 1, characterized by, that a measure of the temperature of the reagent dosing system (30) is recorded when the control unit (26) is started and that the measure of the temperature is taken into account when deciding whether to continue emptying the reagent dosing system (30). [3] Method according to claim 1 or 2, characterized by , that a measurement of the temperature of the reagent dosing system (30) is recorded when the control unit (26) is started and that operation of the reagent dosing system (30) is permanently prevented if the measurement of the temperature falls below a temperature threshold. [4] Method according to claim 3, characterized by, that each instance of falling below the temperature threshold in a reagent dosing system (30) that is not completely emptied is counted and stored in the memory (32) of the control unit (26) and that operation of the reagent dosing system (30) is only permanently prevented if the number of instances exceeds a threshold value. [5] Device for operating a control unit which controls a reagent dosing system (30) arranged in a motor vehicle, characterized by that the control unit (26) is a specially prepared control unit (26) for carrying out the method according to one of the preceding claims 1-4. [6] Control unit program that performs all steps of a method according to any one of claims 1-4 when it is executed in a control unit (26). [7] Control unit program product with program code stored on a machine-readable medium for carrying out the method according to any one of claims 1-4 when the program is executed in a control unit (26).

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