Methods for calibrating and operating pumps

Abstract

The present invention relates to a method for calibrating a pump having a pump chamber, two valves for the pump chamber and being electrically powered, at least one of the valves being actively controllable, wherein the electric motor can cause an element defining the pump chamber to move back and forth, wherein the pump chamber is pressurized with a compressible medium, wherein at least one rotation of the rotor is accomplished by the electric motor, and different angular positions of the rotor are detected, wherein a change in the pressure (p) of the medium in the pump chamber is detected (V3) during at least one rotation of the rotor, and wherein a correlation is established between the position (h) of the element defining the pump chamber and the angular position (h) of the rotor based on the pressure change (V3), and a method for operating the pump.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for calibrating a pump of an SCR supply system, a method for operating such a pump and a computing unit and a computer program for carrying out the method. BACKGROUND

[0002] In the aftertreatment of exhaust gases in motor vehicles, the so-called SCR method (English: Selective Catalytic Reduction) can be used, in particular for the reduction of nitrogen oxides (NOx) x Here, an aqueous urea solution (HWL) is introduced as a reducing agent solution into the exhaust gas, which typically has a high oxygen content.

[0003] For this purpose, a metering module or a metering valve can be used, which comprises a nozzle for spraying or introducing the aqueous urea solution into the exhaust gas stream. Upstream of the SCR catalyst, the aqueous urea solution reacts to ammonia, which then combines with the nitrogen oxides at the SCR catalyst, thereby forming water and nitrogen.

[0004] The metering valve is typically connected to a pump via a high-pressure line. The pump pumps the aqueous urea solution from a reducing agent tank to the metering module. In addition, a return line is mostly connected to the reducing agent tank, via which excess aqueous urea solution can be conducted back. A throttle plate or a throttle valve in the return line can control the backflow. SUMMARY

[0005] According to the invention, a method for calibrating a pump, a method for operating a pump and a computing unit and a computer program for carrying out the method are proposed with the features of the independent patent claims. Advantageous configurations are the dependent claims and the subject matter described subsequently.

[0006] The invention discusses a pump, which has a pump chamber and an electric motor, the pump chamber having two valves for the pump chamber, at least one of the valves, however advantageously both valves, being actively controllable, with the electric motor it is possible to move an element defining the pump chamber back and forth (or up and down). The element can preferably be a diaphragm, which is coupled, for example via a connecting rod, to an eccentric wheel arranged at the rotor of the electric motor. In this case, a so-called diaphragm pump as typically used in the already mentioned SCR supply system is then involved. However, in principle the element does not have to be a diaphragm; a piston which (directly) defines the pump chamber is also conceivable. Here, the two valves are used in particular as inlet valve and outlet valve.

[0007] An actively controllable valve, which applies not only to the inlet valve but also to the outlet valve, is to be understood in this case as a valve which can be actively and purposefully caused to open and close, for example by means of a magnetic switch or by means of an electromagnet. In contrast thereto, other valves, which are also used conventionally in SCR systems in pumps, are valves which open passively or automatically when a certain pressure is applied. Thus, with such a conventional valve, for example, fluid can be sucked into the pump chamber in the intake phase of the pump by means of the inlet valve and then pressed out of the pump chamber in the pumping or delivery phase by means of the outlet valve (in the case of a closed inlet valve).

[0008] A particular advantage of a pump with actively controllable valves is that the pump can be operated in more or less arbitrary fashion by means of the individual actuation of the valves, for example also in a delivery direction which is opposite to the normal delivery direction. This can mean in an SCR supply system, for example, that fluid, such as an aqueous urea solution, can also be delivered from the metering module back into the fluid tank if required, wherein the fluid is delivered from the fluid tank to the metering module in the SCR supply system. For this purpose, it is only necessary to open and close the valves in a corresponding manner. This delivery direction which is opposite to the normal delivery direction is advantageous in particular in the case of an SCR supply system, because there the fluid, or then the aqueous urea solution, can be delivered from the metering module back into the fluid tank after the internal combustion engine or diesel engine has been switched off, in order to prevent freezing, in particular in winter.

[0009] However, in order to be able to achieve the best possible operation of the pump, it should always be known as precisely as possible the current position of the elements which define the pump chamber, in order to be able to actuate the valves accordingly on the basis thereof. It is thus possible, for example, to open or close the valves exactly at the time when the maximum volume of the pump chamber is reached or also purposefully after a certain time.

[0010] The application proceeds here and proposes that the pump chamber is first pressurized with a compressible medium. As a medium, a gas or a gas mixture is considered here, in particular. Then, at least one revolution of the rotor is completed with the electric motor (two or three or still more revolutions are also conceivable, of course), and the different angular positions of the rotor are detected. This is preferably carried out by means of one or more magnetically sensitive elements, for example Hall sensors, in the electric motor, which can have the magnetically sensitive elements, for example, for controlling the commutation. However, the use of an incremental encoder is also conceivable. The specific type here ultimately also depends on the type of electric motor used. For a more detailed explanation and example, reference is also made at this point to the drawing description.

[0011] During at least one revolution of the rotor, the course of the pressure of the medium in the pump chamber is detected. For this purpose, it is possible to use, for example, a pressure sensor which is already present at the pump anyway (this is often the case, for example, in the case of a pump for an SCR supply system). However, it is of course also conceivable to use an additional or separate pressure sensor or pressure measuring device. It goes without saying that the pump chamber should be closed here, if necessary together with the lines connected thereto, so that the pressure changes caused by the movement of the elements delimiting the pump chamber can be detected with the pressure sensor.

[0012] A correlation is then established between the course of the pressure and the angular position of the rotor and, if necessary, of the position of the element delimiting the pump chamber. This correlation can be stored on a computing unit which is provided for operating the pump. In this way, for example when the pump is initially assembled in a vehicle or in a separate delivery unit, a corresponding relationship between the angular position of the rotor and the position of the element delimiting the pump chamber can be established and used for targeted actuation of the valve. The engine regulator (logic circuit) of the pump itself, that is to say, for example, a microcontroller or the like, is suitable for this purpose. If the pump has its own logic circuit, in particular for controlling the electric motor, the determined correlation can be stored in a memory unit of the pump logic circuit, for example an EEPROM, a flash memory or the like. The entire pump unit can thus be replaced, in particular when repairing, since all data for exactly this unit are stored directly on the unit. The superordinate control device only still sends requests such as rotational speed, if necessary opening and closing angle or efficiency.

[0013] It is expedient here for the latency time to be taken into account when detecting the pressure in the case of establishing the correlation, as this occurs, for example, due to signal run times and / or delays when the pressure change propagates.

[0014] It is particularly preferred for an additional angular position of the rotor to be detected which corresponds to a predetermined position of the element delimiting the pump chamber and to be taken into account in the correlation. Thus, the synchronization of the course of the angular position and the course of the pressure can be carried out particularly simply and quickly. This is particularly advantageous if the additional angular position is not included in the different detected angular positions of the rotor, for example because there is no angular position sensor system for this purpose.

[0015] The additional angular position is preferably detected on the basis of a current flow in the electric motor which corresponds to a predetermined position of the element delimiting the pump chamber, wherein the predetermined position of the element delimiting the pump chamber corresponds to a minimum volume of the pump chamber. The latter is usually the case at the bottom dead centre. This action is based on the fact that a slightly higher torque of the electric motor is usually required for the compression of the medium, which is noticeable by an increased current flow.

[0016] Alternatively or additionally, it is also preferred that, upon pressurization of the pump chamber, an additional angular position is reached by letting the motor run down, wherein the predetermined position of the element defining the pump chamber corresponds to the maximum volume of the pump chamber. The latter is usually the case at top dead center. This action is based on the fact that the element defining the pump chamber will be moved by the medium under pressure in the pump chamber such that the volume of the pump chamber becomes maximum. Without external torque, the rotor will follow this movement.

[0017] As already mentioned, the correlation established in this way between the position of the element defining the pump chamber and the angular position of the rotor enables targeted manipulation of the valves of the pump. In this sense, a further aspect of the application is a method for operating a pump as set forth above. Here, during operation of the pump, at least one actively manipulable valve is manipulated in accordance with the position of the element defining the pump chamber such that the pump is operated with less than maximum possible efficiency.

[0018] That is, by targeted variation of the opening and closing times of the valves, the efficiency of the pump can be varied. This has the advantage that the pump as a whole (valves on the suction side, diaphragm, valves on the pressure side) has very good dynamics. Thus, the pump can always be operated with non-optimal efficiency (valves on the suction side and on the pressure side do not open or close at the optimal point with respect to the working pressure). If a quantity jump (increase or, if necessary, decrease in the quantity to be delivered) is requested by, for example, a superordinate control system, this can first of all be done by varying the efficiency of the pump system. In this respect, the valve control device generally reacts much faster than the motor of the pump can be accelerated or braked. A much higher and much more precise dynamic adjustment of the system can thus be achieved. The motor can also be designed to be (relatively) slow.

[0019] The computing unit according to the application, for example a control device of a motor vehicle, for example an engine control device or an exhaust gas aftertreatment control device or a pump control device, for example a control and / or regulating unit of a motor of a pump, is in particular set up in terms of programming technology for carrying out the method according to the application.

[0020] The implementation of the method according to the application in the form of a computer program or computer program product with program code for carrying out all the method steps is also advantageous, since this leads to particularly low costs, in particular when the control device in which the implementation takes place is also used for other tasks and is therefore present anyway. Suitable data carriers for providing the computer program are in particular magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs, etc. It is also possible to download the program via a computer network (Internet, Intranet, etc.).

[0021] Further advantages and configurations of the application result from the description and the attached drawings.

[0022] The application is schematically illustrated in the drawings according to embodiments and is described below with reference to the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 A fluid supply system with a pump is schematically illustrated, in which the method according to the application can be implemented.

[0024] Figure 2 A pump is schematically illustrated, in which the method according to the application can be implemented.

[0025] Figure 3 A flow of the method according to the application in a preferred embodiment is schematically illustrated.

[0026] Figure 4 An electric motor for a pump is schematically illustrated, with which the method according to the application can be implemented. DETAILED DESCRIPTION

[0027] In Figure 1 A fluid supply system 100 configured as an SCR supply system is schematically and exemplarily illustrated in Fig. 1, in the case of which fluid supply system or in the case of the pump present there, the method according to the application can be implemented. The SCR supply system 100 comprises a pump or delivery pump 210, which has a pump chamber 220, two actively controllable valves 221 and 222 for the pump chamber 220 and has a filter 230. These components together exemplarily constitute a delivery unit 200, which can be provided, for example, as a structural unit.

[0028] Here, in the case of a normal delivery direction, the valve 221 serves as an inlet valve and the valve 222 serves as an outlet valve. In addition, the pump 210 has a delivery element 225 in order to increase and decrease the volume of the pump chamber 220. The delivery element 225 can be, for example, a membrane, as this is set out in more detail below.

[0029] The pump 210 is now set up for delivering the reducing agent 121 (or reducing agent solution) as a fluid to be delivered from a fluid tank 120 via a high-pressure line 122 to a metering module or metering valve 130. There the reducing agent 121 is then injected into an exhaust branch 170 of an internal combustion engine.

[0030] In addition, a pressure sensor 140 (which may also be installed in the delivery unit 200) is provided, which is configured to measure the pressure at least in the high-pressure line 122. For example, a computing unit 150 configured as an exhaust aftertreatment control device is connected to the pressure sensor 140 and obtains information about the pressure in the high-pressure line 122 from the pressure sensor. Furthermore, the exhaust aftertreatment control device 150 is connected to the delivery unit 200, and therein particularly to the pump 210, and to the metering module 130, for the purpose of controlling it.

[0031] Furthermore, the SCR supply system 100 exemplarily includes a loop 160 through which the reducing agent can be guided from the system back to the fluid tank 120. An exemplarily arranged throttle plate or valve 161 is provided in this loop 160, which provides local flow resistance. However, it should be noted that this loop can be omitted in the case of a pump with an actively controlled valve.

[0032] Exhaust aftertreatment control equipment is configured to coordinate the system's actuators based on relevant data, such as data received from engine control equipment or sensors for temperature, pressure, and nitrogen oxide content in the exhaust, to introduce a urea solution into the exhaust manifold (Abgastrakt) in front of the SCR catalyst according to the operating strategy. Furthermore, on-board diagnostic (OBD) systems, for example, monitor components and parts of the exhaust aftertreatment system related to compliance with exhaust emission limits.

[0033] exist Figure 2 Sectional view and in Figure 1 The pump 210 is illustrated in more detail in the figure, in which the method according to the invention can be implemented. In addition to the pump chamber 220 and two actively controllable valves 221 and 222 for the pump chamber 220, the pump 210 has in particular an element 225 configured as a diaphragm that defines the pump chamber 220.

[0034] In addition, a motor 240 is provided, and a connecting rod 250 is provided, for example by means of an eccentric wheel (see angle for details). The diaphragm 225 is mounted on the rotor 245 of the motor 240, and the connecting rod is also connected to the diaphragm. In this way, the up-and-down movement of the diaphragm 225 can be achieved by the rotational movement of the rotor 245.

[0035] Here, the two valves 221 and 222 are exemplary to have electromagnets by means of which the appropriate elements can be operated to release flow, i.e., open or close the valve.

[0036] exist Figure 3The diagram schematically illustrates the flow of the method according to the invention in a preferred embodiment. For this purpose, the pump stroke h (e.g., diaphragm stroke) is plotted as the position of the elements defining the pump chamber over time t in three superimposed graphs. The pressure p of the medium in the pump chamber over time t is also plotted in the lower graph. At a constant rotational speed, time t corresponds to the rotor angle or rotational speed. (See also: for this purpose) Figure 2 Here, the stroke h varies between the top dead center OT and the bottom dead center UT, wherein the pump chamber has its maximum volume in the OT case and its minimum volume in the UT case.

[0037] The process V1 in the above diagram now shows the delivery of fluid by means of a pump, where points A, B, C, and D indicate the position of the stroke and thus the current volume of the pump chamber, at which one of the valves is operated (opened or closed).

[0038] For better understanding, the two valves should be referred to below as the inlet valve and the outlet valve, with fluid flowing into the pump chamber through the inlet valve and out through the outlet valve. Normal and reverse flow operate in the same manner, with the inlet valve positioned on the side of the fluid tank and the outlet valve positioned on the side of the metering module during normal flow. This is reversed during reverse flow.

[0039] At point A, the pump chamber (with at least substantially maximum volume) is filled with fluid. The outlet valve is initially still closed, but is opened at point A. The inlet valve is closed and remains closed. Thus, fluid is pumped out of the pump chamber.

[0040] At point B, the fluid is then at least substantially completely discharged from the pump chamber (complete evacuation would be practically impossible). The outlet valve is then closed. Immediately thereafter, or perhaps very shortly after, at point C, the inlet valve, which was closed initially, is opened, while the outlet valve remains closed.

[0041] Thus, fluid is drawn into the pump chamber along the OT direction. Upon reaching OT, the inlet valve closes at point D. The pump chamber is then filled with fluid. This process is then repeated from point A.

[0042] In order to operate the pump at a lower efficiency, as also proposed within the scope of this invention, the outlet valve cannot be opened at OT or shortly after OT, but only slightly later, as indicated by point A'. Less fluid is delivered in this manner, but by advancing the opening of the outlet valve in time (e.g., to point A), the delivered volume and thus efficiency can be rapidly increased.

[0043] Another preferred possibility is, for example, to open the outlet valve at OT or shortly after OT, but close it before reaching UT, that is, to advance point B to, for example, point B', so that not all fluid can be discharged from the pump chamber. Similarly, in the case of the inlet valve, a corresponding change can be made to, for example, open the inlet valve later or close it earlier, so that less fluid has been drawn into the pump chamber.

[0044] However, for such targeted manipulation, the correlation between the diaphragm position or stroke and the rotor angular position should be known. The establishment of this correlation is described below in different preferred variations.

[0045] After assembling the pump or complete delivery unit, the entire system (i.e., the delivery unit, especially with the necessary computing unit) is calibrated. This can be done within the delivery unit or as a single pump module. For this, the active suction side valve can be closed, while the outlet side valve can be opened. On the outlet side, compressed air or other compressible gas or gas mixture is loaded into the pump module or pump chamber. A pressure sensor is placed on the pressure side, for example, in… Figure 1 As shown. However, it is also possible to use a pressure sensor located in the installed delivery unit to measure the pressure.

[0046] Advantageously, the medium under pressure should not be overly compressible, as this could potentially lead to an excessively small deviation (Ausschlag) in the pressure sensor's output signal. If the medium is not very compressible, a larger deviation will result in the pressure signal. Additionally, the introduced pressure should roughly correspond to the system's rated pressure (when the entire system is running later), as this maximizes the accuracy of the pressure sensor and ensures optimal offset (Auslenkung) in the output signal.

[0047] In some cases, it would be sufficient if the pump itself built up the required pressure through its operation. In principle, this would correspond to a compressor used for compressed air, which itself builds up the necessary pressure. However, this is only suitable when a certain basic alignment already exists between the motor or rotor and the connecting rod or diaphragm (e.g., during assembly), where the inlet and outlet valves must also be operated in time-coordinated with the connecting rod position.

[0048] Typically, the connecting rod is pushed upwards by the pressure in the pump chamber. However, it is also possible that the connecting rod is precisely at bottom dead center (UT), so that it will not move. Therefore, the motor is switched on or started, and the motor is induced to begin rotating. In this case, it is not relevant to how many times the rotor rotates, i.e., how many revolutions the rotor completes; rather, it is advantageous to induce the motor to end its rotation by a jogging operation. For this purpose, the motor does not actively brake the rotational motion; more precisely, the motor decelerates and stops the rotational motion. Through this action, the rotor (due to the pressure in the pump chamber) comes to a stop, causing the connecting rod (and therefore the diaphragm) to be at top dead center (OT or 0°). Although this point can be omitted for connecting rod position identification, it simplifies the method.

[0049] As a next step, the rotor is (again) put into rotation. At least two revolutions are advantageous here. The rotational speed should be fast enough to achieve smooth rotor movement, otherwise the motor will be operated in step-by-step mode. However, in principle, this possibility of step-by-step control is also conceivable. However, the rotor should not rotate too fast, as this may result in slip during measurement.

[0050] In parallel with the control electric motor, pressure is detected using a pressure sensor located in the pressure-side region of the system. The electric motor typically has a Hall sensor or other magnetically sensitive or magnetosensitive element for determining the moment of commutation. These Hall sensors are typically digital Hall sensors, which are, for example, mounted on a circuit board of the engine electronics. For example, three Hall sensors are provided, arranged accordingly with respect to the rotor.

[0051] These Hall sensors detect changes in the rotor's magnetic field. These changes are formed by the magnetic field (poles) swept along by the Hall sensors as the rotor rotates. If a magnetic field is detected, the Hall sensors emit a signal. In this way, using three Hall sensors, for example, six pulses can be detected for each revolution, resulting in a total of 18 pulses per revolution in a system with three Hall sensors, which in turn means 36 steps per revolution. The exact number of magnetic fields and steps is determined by the specific engine design and is ultimately irrelevant to this invention.

[0052] Using a Hall sensor and a commutation device for the coil, an angle can be constructed through interpolation in the case of an electric motor (Winkdelgrade). Therefore, a sine function can be created and stored for motion via the eccentric wheel. This sine change process... Figure 3The intermediate chart is shown as change process V2. As mentioned above, the signal output by the Hall sensor corresponds to the angular position of the rotor, one of which is exemplarily represented by... express.

[0053] Now, the synchronization or correlation between this mathematical sinusoidal change process and the connecting rod or diaphragm is achieved via a pressure sensor or by detecting the pressure or pressure change process of the medium in the pump chamber. For this purpose, reference should be made to... Figure 3 The following chart shows, in addition to the change process V2, various measured values ​​p. i The process of pressure change, V3.

[0054] Because the connecting rod presses the diaphragm downwards, the movement of the connecting rod causes an increase or change in pressure within the pump chamber. Therefore, the pressure within the pump chamber follows the movement of the connecting rod, which in turn follows the rotor via the eccentric wheel, and the rotor follows commutation. Commutation is, for example, followed by motor control pre-defined by software, which follows an interpolated sinusoidal process. In this way, the motor knows the connecting rod positioning and the commutation or rotor position.

[0055] However, it is also necessary to pay attention to time offset when necessary, such as in Figure 3 The following chart uses t D This can be seen. For example, this involves the system's latency. This latency is primarily determined by the pressure sensor. The pressure sensor has an internal processing time for reading the internal pressure measurement unit, quantifying, and transmitting the data. The receiver of the data may also have a time offset, which should also be considered.

[0056] If the pressure sensor installed in the conveying unit must be read by the control device as a component, and then the data must be transmitted to the motor via a bus, such as CAN, then particularly high latency can be envisioned. However, this is readily apparent within the scope of the initial creation of the correlation (“initial training”), because in this case the control device (or inspection and calibration computer) can react better and faster, and provide the data stream to the motor without jitter or latency fluctuations. For this reason, a slower speed is advantageous, as latency and jitter have a minimal impact proportionally.

[0057] After pressure sensor measurements have been evaluated, for example, in an electric motor in relation to rotor position, these data can be stored, which may be needed later to convert rotor motion into link position.

[0058] For example, two commutation processes can be synchronized by considering the maximum current required to overcome the bottom dead center (BDC) at which the highest compression occurs in the pump chamber. This point can also be used as a second starting point (Anhaltspunkt) (and thus as an additional angular position) (the point with the highest commutation current during a single rotation). Therefore, this point can be entered into the calculations as a reference, and rotations can be performed with defined points, where positioning or position evaluation can be involved. Using these two points, it can be identified at any time which commutation point the connecting rod is located at. At the end of the calibration process, the motor can store this data in its memory or the memory of the corresponding computing unit so that the data is permanently stored even after the supply voltage is cut off.

[0059] If, due to factors such as blockage or other malfunctions, the motor skips commutation in the conveyor unit during actual operation, the system efficiency deteriorates because the active valve is no longer correctly open or closed relative to the linkage position. This can be observed. Therefore, a control device can, for example, instruct the motor to recalculate using the last valid value from calibration. However, if this does not improve system efficiency, the control device can, for example, instruct the motor to begin a new calibration.

[0060] However, it is preferable not to immediately write the data obtained through this new calibration into the non-volatile memory, but only when an efficiency improvement occurs. The invitation to write this new calibration data into the non-volatile memory is, for example, initiated by a command from the control device to the motor.

[0061] In principle, motor wiring with an incremental encoder is safer for the process because it allows for a finer evaluation of angular amplitude or angular position. However, this is only applicable if the incremental encoder provides a finer resolution than the 36 pulses or 10° subdivisions per revolution from the previously illustrated example. Particularly convincing is achieved if the motor then still has the capability to generate a single pulse per revolution (as an additional angular position).

[0062] In this scenario, calibration or training appears similar to the aforementioned process. In the assembled state, the medium in the pump chamber is pressurized, the motor runs the rotor for several rotations, the pressure is detected, the pressure data is interpolated, the rotational data is correlated with the pressure sensor data, and an angular offset (mapped in the pressure signal) can be established between the rotor and connecting rod positions, and the correlation can be stored. However, if an additional single pulse is present per rotation via an incremental encoder, analysis of current, etc., is unnecessary. This single pulse can be delegated to the control device, providing safety by determining the absolute position even in the event of commutation losses.

[0063] In systems that use analog Hall sensors instead of digital ones, or magnetic encoder chips with Hall sensor emulation and control magnets, very high-quality qualitative statements can be obtained. In this case, a two-pole, correspondingly magnetized ring magnet can be fixedly mounted to the rotor shaft or rotor (e.g., by bonding or pressing). The magnetic encoder chip on the circuit board can then identify the magnetic field and assign the angular position to the rotor's rotation angle.

[0064] The system must first be learned (the rotation angle of the control magnet to the rotation angle of the rotor magnet to the position of the stator). Advantageously, the control electronics know the rotor's rotation angle position at all times and can easily and reliably establish a correlation between the pressure sensor and the linkage position. Therefore, in this variant, the system only needs to be learned once. Recalibration of the linkage position relative to the rotor position is no longer required.

[0065] exist Figure 4 The diagram shows an electric motor 240' having an annular magnet 260 and a magnetic encoder chip with a Hall sensor emulation 265 on, for example, a circuit board 266 (left in the top view, right in the cross-sectional view). Here, the annular magnet 260 is mounted on a rotor shaft 280 of a rotor 245' configured as a bell.

Claims

1. A method for calibrating a pump (210) having a pump chamber (220), two valves (221, 222) for the pump chamber (220) and having an electric motor (240), at least one of the valves being actively controllable, with the electric motor it is possible to move an element (225) defining the pump chamber (220) back and forth, wherein the pump chamber (220) is pressurized with a compressible medium, wherein a change curve (V3) of the pressure (p) of the medium in the pump chamber (220) is detected during at least one revolution of the rotor (245), and wherein the additional angular position is detected based on a through current in the electric motor (240) corresponding to a predetermined position of the element (225) defining the pump chamber (220).

3. The method according to claim 1 or 2, wherein the additional angular position is detected based on a through current in the electric motor (240) corresponding to a predetermined position of the element (225) defining the pump chamber (220), wherein the predetermined position of the element defining the pump chamber corresponds to a minimum volume of the pump chamber (220). wherein at least one revolution of a rotor (245) thereof is accomplished with said electric motor (240) and different angular positions of said rotor are detected }, 4. The method according to claim 1 or 2, wherein the additional angular position is reached by stopping the electric motor (240) decelerated during pressurization of the pump chamber (220), wherein the predetermined position of the element (225) defining the pump chamber corresponds to a maximum volume of the pump chamber. wherein a correlation is established between the position (h) of the element (225) delimiting the pump chamber (220) and the angular position (a) of the rotor as a function of the pressure variation (V3) ) wherein in addition an additional angular position of the rotor (245) is detected which corresponds to a predetermined position of an element (225) defining the pump chamber (220), and the additional angular position is taken into account in case of a correlation between the position (h) of the element (225) defining the pump chamber (220) and the angular position of the rotor (a) ) wherein the predetermined position of the element defining the pump chamber corresponds to a bottom dead center or a top dead center.

2. The method according to claim 1, wherein in case the correlation is established, a latency (t D ) is taken into account when detecting the pressure.

8. The method according to claim 1 or 2, wherein a correlation between the position (h) of the element (225) defining the pump chamber and the angular position of the rotor is stored on a computing unit (150) provided for operating the pump (210).

9. The method according to claim 1 or 2, wherein the pump (210) is used in an SCR supply system (100).

5. The method according to claim 1 or 2, wherein the different angular positions of the rotor (245) are detected by means of one or more magnetically sensitive elements in the electric motor (240) .

6. The method according to claim 5, wherein the different angular positions of the rotor (245) are detected by means of Hall sensors in the electric motor (240) .

7. The method according to claim 1 or 2, wherein the different angular positions of the rotor are detected by means of an incremental encoder. ).

10. A method for operating a pump (210) for delivering a fluid (121) using a method according to any one of claims 1 to 9, the pump having a pump chamber (220), two controllable valves (221, 222) for the pump chamber (220) and having an electric motor (240), at least one of the valves being actively controllable, with the electric motor it is possible to move an element (225) defining the pump chamber back and forth, wherein during operation of the pump (210) at least one actively controllable valve (221, 222) is operated in accordance with the position (h) of the element (225) defining the pump chamber, so that the pump (210) is operated with less than maximum possible efficiency.

11. The method according to claim 10, wherein the method is used for operating a pump (210) for delivering a fluid (121) in an SCR supply system (100).

12. The method according to claim 10, wherein the pump (210) is calibrated according to any one of claims 1 to 9.

13. A computing unit (150) which is set up for carrying out all method steps of a method according to any one of claims 1 to 9. ​ ​ ​ 14. A computer program product comprising a computer program which, when implemented on a computing unit (150), causes the computing unit (150) to implement all the method steps of the method according to any one of claims 1 to 9.

15. A machine readable storage medium having stored thereon the computer program comprised in the computer program product according to claim 14.

16. A computing unit (150) arranged to implement all the method steps of the method according to any one of claims 10 to 12.

17. A computer program product comprising a computer program which, when implemented on a computing unit (150), causes the computing unit (150) to implement all the method steps of the method according to any one of claims 10 to 12.

18. A machine readable storage medium having stored thereon the computer program comprised in the computer program product according to claim 17.

Images