Method for operating a pump

Abstract

This invention relates to a method for operating a pump having a pump chamber, two valves for the pump chamber, wherein at least one valve has an electromagnetic actuator including a coil and an armature and is therefore actively controllable, and the pump also has an electric motor by which elements limiting the pump chamber can be reciprocated, wherein, during the suction phase (P... A In order to open at least one actively controllable valve, the valve coil is energized at least until a first current intensity (I1) is reached, wherein, during the closing phase (P... S In the process, the current in the coil is reduced, thereby closing the valve; and in the attraction phase (P) A ) and closing phase (P S Between ) in the maintenance phase (P) H In the first current, the coil is energized at an average second current intensity (I2) less than the first current intensity to keep the valve open, and / or the current in the coil is reduced at least temporarily by means of rapid quenching (S).

Description

Technical Field

[0001] The present invention relates to a method for operating a pump, such as an SCR supply system, as well as a computing unit and a computer program for implementing the method. Background Technology

[0002] In the aftertreatment of exhaust gases from motor vehicles, especially to reduce nitrogen oxides (NOx), the so-called SCR (Selective Catalytic Reduction) method can be used. In this case, a urea-water solution (HWL) is introduced as a reducing agent into the typical oxygen-rich exhaust gases.

[0003] For this purpose, a dosing module or dosing valve can be used, which includes nozzles, to inject or carry the urea-water solution into the exhaust gas stream. Upstream of the SCR catalyst, the urea-water solution reacts to form ammonia, which then combines with nitrogen oxides at the SCR catalyst to produce water and nitrogen.

[0004] The dosing valve is typically connected to a pump via a pressure line. The pump dispenses the urea-water solution from the reducing agent tank to the dosing module. Additionally, in most cases, a return line is connected to the reducing agent tank, through which excess urea-water solution can be returned. Orifices or throttling devices in the return line control the return flow rate. Summary of the Invention

[0005] According to the present invention, a method for operating a pump, a computing unit for implementing the method, and a computer program are provided. Advantageous designs are the subject of this invention.

[0006] A method for operating a pump, the pump having a pump chamber, two valves for the pump chamber, wherein at least one valve has an electromagnetic actuator including a coil and an armature and is therefore actively controllable, the pump also having an electric motor by means of which an element limiting the pump chamber is capable of reciprocating motion, wherein, in the suction phase, in order to open at least one actively controllable valve, the coil of the valve is energized at least until a first current intensity is reached, wherein, in the closing phase, the current in the coil is reduced, thereby closing the valve; and wherein, between the suction phase and the closing phase, in the holding phase (P... H In this process, the coil is energized on average with a second current intensity less than the first current intensity to keep the valve open, and / or the current in the coil is reduced at least temporarily by means of rapid quenching, wherein the current in the coil is passively reduced by means of an idle diode.

[0007] As described above, in the method of operating a pump according to the present invention, the pump has a pump chamber with two valves for the pump chamber, at least one, but preferably both, valves being actively controllable. An electric motor is also provided, which can reciprocate (or move up and down) an element that limits the pump chamber. This element can preferably be a diaphragm, which is coupled, for example, via a connecting rod to an eccentric wheel disposed at the rotor of the electric motor. In this case, it is a so-called diaphragm pump, as typically used in the SCR supply system already mentioned. In principle, the element does not necessarily have to be a diaphragm; a piston, which (directly) limits the pump chamber, can also be considered. The two valves here are specifically used as an inlet valve and an outlet valve.

[0008] An actively controllable valve (this applies not only to inlet valves but also to outlet valves) is understood in this context as one that can be actively and purposefully opened and closed, more precisely, via an electromagnetic actuator with a coil and armature, so that the valve can be switched by energizing the coil. In contrast, other valves—or those commonly used in pumps in SCR systems—open passively or automatically upon the application of a defined pressure. This common type of valve can also be used, for example, to draw fluid into the pump chamber through the inlet valve during the pump's suction phase and then, during the pumping or delivery phase, to expel it from the pump chamber through the outlet valve—with the inlet valve closed.

[0009] A particular advantage of pumps with actively controllable valves is that the pump can be operated in more or less arbitrary ways through personalized valve operation; for example, it can be operated in a delivery direction opposite to the conventional delivery direction. This, in an SCR supply system (where fluids such as urea-water solutions are delivered from the fluid reservoir to the metering module), means, for example, that the fluid can also be returned from the metering module to the fluid reservoir when needed. This can be achieved simply by opening and closing the valve accordingly. A delivery direction opposite to the conventional delivery direction is particularly advantageous in SCR supply systems because there, after the internal combustion engine or diesel motor stops, the fluid—e.g., urea-water solution—can be returned from the metering module to the fluid reservoir to prevent freezing, especially in winter.

[0010] The efficiency of a pump can also be altered, for example, by selectively changing the opening and closing times of valves. This has the advantage that the pump as a whole (valves on the suction side, diaphragm, and valves on the pressure side) possesses particularly good dynamic characteristics. Thus, the pump can always operate at suboptimal efficiency (the valves on the suction side and pressure side are not opening or closing at their optimal points with respect to operating pressure). If, for example, a higher-level control system requires a sudden change in quantity (increasing or, in some cases, decreasing the quantity to be delivered), this can be achieved immediately by changing the efficiency of the pump system. Valve control in this regard can typically react much faster than the acceleration or deceleration of the pump's electric motor. This allows for much higher and more precise dynamic regulation of the system. The electric motor can also be designed to be (relatively) slow.

[0011] Given the unique operation of pumps, especially when using actively controllable valves, the problem often lies in the inaccurate timing of opening and closing two or at least one valve. This can cause pressure spikes (on the pressure side). If the pressure in the pump chamber exceeds the pressure on the pressure side (because the pressure-side valve opens too late), the medium or fluid can surge to the pressure side of the system, potentially damaging components on that side, such as pressure fittings. If a valve opens unintentionally too early, the medium can flow back into the pump chamber, potentially causing a short-term pressure drop. Similar problems arise with the valves on the suction side. If they open too late, cavitation can occur due to negative pressure in the pump chamber; if they open too early, compressed medium can be expelled from the pump chamber towards the suction channel. If two valves open overlapping, the pressure on the pressure side can be reduced towards the suction side, potentially leading to a hydraulic short circuit in extreme cases.

[0012] Therefore, it is desirable to operate actively controllable valves reliably and controllably, in which pressure fluctuations, temperature fluctuations (introduced from the outside or caused by unwanted activation), or other effects such as manufacturing tolerances of valve actuators, such as internal resistance, sensitivity, and lift, can be observed and compensated.

[0013] Furthermore, there are operating conditions under which the coil should or must be switched particularly accurately and quickly, or the coil must be activated for a longer period of time. For example, at low speeds in an electric motor, longer activation time is required. To ensure that the valve behaves as neutrally as possible to the upstream control unit, it should be ensured through the presentation of the current curve, the knowledge of the current physical parameters, and skillful operation that the coil maintains its (controllable) characteristics at all times, even under varying operating parameters (long or short opening times, temperature, voltage), without negatively impacting the system.

[0014] System evaluations or measurements have shown that the control time of each active valve is significantly altered by the rotational speed of the pump's electric motor. Furthermore, factors such as supply voltage or coil temperature also affect behavior over time. Changing rotational speeds result in different opening times even in an ideally designed pump system. At lower speeds (e.g., approximately 500 U / min), opening times are, for example, approximately 30 ms, while at higher speeds (e.g., approximately 2000 U / min), opening times are, for example, approximately 7.5 ms.

[0015] If the system operates at or near a low operating voltage, the current in the coil increases relatively slowly, delaying the valve's opening; conversely, at a high operating voltage, the current in the coil increases relatively quickly, causing the valve to open earlier. In this case, a certain linearity can be assumed. (Over a constant time) double the voltage corresponds, for example, to approximately double the current. This, in turn, means that (energy applied in the magnetic field, sufficient to exert a magnetic force to move the armature in the valve) approximately (in erster) It reaches the switching point at approximately twice the speed. Since the supply voltage is typically between 10V and 30V, it is particularly important to calculate the time from the start of energization until the mechanical movement of the valve or its armature.

[0016] Furthermore, the coil's internal resistance (electrical) has a significant impact. The internal resistance of the coil wires changes with temperature. Additionally, the activation of the active valve causes the coil wires to heat up. If the coil is frequently or for extended periods, or at high switching voltages, it heats up and thus alters the current rise curve. Consequently, the time between energization and armature movement is also prolonged. If the energy stored in the active valve or its coil must be removed or eliminated again at the end of energization, the same output as at the beginning of energization occurs.

[0017] If the energy potential is high at the turn-off time, it will take a longer time to reduce the energy stored in the magnetic field to a level where the coil's magnetic field is small enough for the valve armature to fall back into its seat. The coil's temperature (and its internal resistance) also play a significant role in quenching the circuit. The same applies to the voltage within.

[0018] Furthermore, designing coils over a wide voltage range, which is indirectly related to current (and also magnetic force), is particularly difficult. Its performance (rapid triggering upon energization) and the magnetic force used to apply the force to move the armature must be considered. To enable the coil to operate even at low operating voltages, it is typically designed with very low resistance, which in turn is detrimental at high operating voltages, i.e., very high currents, as the coil enters its magnetic saturation.

[0019] Analysis or measurements of pumps with actively controllable valves and conventional coil energization (which ends when armature movement begins) at different operating voltages and speeds have determined the minimum possible opening duration of the valve—despite shutting off the energizer as early as possible and, if necessary, using a freewheeling circuit or rapid quenching. The reduced current in the coil results in a longer on-time than ideal or optimal at high speeds.

[0020] Ideal or optimal opening durations can be achieved at low speeds, which are correspondingly longer than at high speeds. However, this presents another problem. With prolonged valve operation (the optimal opening duration is approximately 30 ms at, for example, around 500 U / min), the coil will enter magnetic saturation. This results in a current that is limited only by the coil's ohmic resistance. In typical coil designs, this leads to relatively high power losses, causing the coil to overheat and potentially damaging the valve (enameled copper wire, coil body, elastomer, thermoplastic, etc.). Furthermore, diodes used for rapid quenching, for example in control electronics, will also overheat significantly as they too begin to unload energy from this level. Similarly, the corresponding output stage supplying the current may also be damaged.

[0021] In the proposed method, during the attraction phase for opening at least one actively controllable valve, the coil is energized at least until a first current intensity is reached. Specifically, the coil is energized during the attraction phase until the armature reaches its terminal position. During the closing phase, the current in the coil is reduced, thereby closing the valve. Furthermore, during the holding phase between the attraction and closing phases, the coil is energized at an average second current intensity less than the first current intensity to keep the valve open, and / or at least temporarily by means of a rapidly quenching voltage, i.e., a voltage polarized opposite to that of the attraction phase, to reduce the current in the coil.

[0022] In this way, the actively controllable valve can operate independently of the rotational speed, preventing damage due to overheating if the holding phase is used with a lower current than usual, and achieving a short opening time through rapid quenching. It is particularly suitable in this regard to use the holding phase when the electric motor speed is below a first threshold, for example, 1,000 U / min, preferably 750 U / min, and to reduce the current in the coil, at least temporarily, by means of rapid quenching, when the electric motor speed is above a second threshold greater than or corresponding to the first threshold. Needless to say, other variations can also be used additionally within the corresponding speed range.

[0023] At the very first moment of energization, i.e., the initiation phase or the anzugsphase, the coil should be charged unimpeded to reach the current required to move the armature as quickly as possible. This is achieved, in particular, by identifying when the armature moves. This can be done, for example, by means of a sensor or acoustically. However, it is also possible to consider (continuously) detecting or measuring the current for this purpose. Typically, armature movement begins at the point where the curve deviates from the e-function (exponential function). Once the curve returns to the e-function, the armature is stopped. After reaching the end position of the armature (e.g., after stopping or after the end of movement), it is preferable to continue energizing for a short period (nachbestromt) to prevent the armature from bouncing (or falling back). This period is also called the post-anzugsphase and occurs between the anzugsphase and the holding phase.

[0024] From this point onward, energization is appropriately (temporarily) terminated because the valve is in a stop position and does not require prolonged energization. During this brief phase, the current in the coil is reduced, for example by means of a freewheeling circuit, particularly to a second current intensity (followed by the so-called freewheeling phase), after which the valve control device (if configured) transitions to a holding phase. In the holding phase, the coil is particularly preferably energized effectively or evenly at a second current intensity by means of PWM control. The holding phase is responsible for keeping the valve open at a (pre-defined) holding current, i.e., the second current intensity. However, it is also entirely possible to transition to the holding phase immediately.

[0025] Then, the valve is closed (if set) by rapid quenching. Alternatively or additionally, the current in the coil can be passively reduced by means of a freewheeling diode, in particular.

[0026] Ideally, the movement of the armature or valve needle should be detected during the closing process. If movement is detected, the actual opening time can be determined. This can be used to allow control software to calculate when or should the energization end, so that the valve truly closes at the desired time.

[0027] All these functions reduce valve heating (but suitably do not exceed the required heat), still keeping the valve quickly in its function and initiating energy quenching at a known level. Quenching at a constant level has the advantage that the stored valve coil energy (in the valve's magnetic field) is maximally small, thus the quenching time is optimally short, and the valve's performance is optimally utilized.

[0028] Furthermore, it is advantageous that the coil is energized, at least temporarily, during the attraction phase using PWM control (rather than continuous control, for example). System evaluation shows that dependence on the supply voltage can be avoided or at least reduced. This allows for a consistently stable and easily controllable relationship. The basis of this control is the system voltage. The valve's magnet is designed for a defined nominal voltage, such as 10V. In this case, the proportions of the pulse width and pause width (i.e., duty cycle) during control can be varied so that the voltage across the coil is always effectively applied at 10V (according to the design). Thus, the energy input (and coil heating) is always constant, as is the fundamental behavior over time in the current performance of armature movement and armature stop. If the valve operates at 20V, a 50% duty cycle can approximately halve the valve voltage. To achieve this improved continuity of the effective valve coil voltage, it is appropriate to monitor the voltage within the system during valve control and track the duty cycle accordingly when changes occur.

[0029] Alternatively, PWM control can be implemented not only with a fixed control frequency and a variable duty cycle, but also with a variable control frequency, such as a fixed pulse width and a variable pause width, or a variable pulse width and a fixed pause width.

[0030] During the holding phase, particularly when using the aforementioned PWM control, it is also preferable to measure the coil temperature. Here, for example, the current can be measured at predetermined time points during the holding phase, at which point the holding current tends to stabilize. The resistance can then be calculated using this current and the voltage applied to the coil (reduced by PWM control). Using this resistance, the temperature or temperature change can be determined based on a reference temperature according to the formula for the temperature coefficient of copper. Such temperature measurement can be used to change the control strategy or check the reliability of the temperature of other systems. It can also be used to completely interrupt control in case of temperature rise, to cool the valve again.

[0031] The computing unit according to the invention, such as a motor vehicle controller, such as a motor controller or exhaust aftertreatment controller or pump controller, such as a control and / or regulation unit for an electric motor of a pump, is particularly configured in terms of programming technology to execute the method according to the invention.

[0032] It is also advantageous to implement the method according to the invention in the form of a computer program or computer program product having program code for performing all method steps, because this results in particularly low costs, especially if the control device used for execution is also used for other tasks and therefore already exists. Suitable data carriers for providing the computer program are, in particular, magnetic, optical, and electrical memories, such as hard disks, flash memory, EEPROM, DVDs, etc. Program downloading via computer networks (Internet, Ethernet, etc.) is also possible.

[0033] Other advantages and design solutions of the present invention are given in the specification and drawings. Attached Figure Description

[0034] The present invention is illustrated schematically with the aid of the embodiments shown in the accompanying drawings, and is described below with reference to the drawings.

[0035] Figure 1 The illustration schematically depicts a fluid supply system with a pump, in which the method according to the invention can be implemented.

[0036] Figure 2 A pump is schematically shown, in which the method according to the invention can be implemented.

[0037] Figure 3 Schematic illustration based on Figure 2 The operation process of the pump.

[0038] Figures 4 to 6 Graphs showing current curves for controlling the valve in accordance with the method according to the invention are shown in different preferred embodiments. Detailed Implementation

[0039] Figure 1 The diagram schematically and exemplary illustrates a fluid supply system 100 configured as an SCR supply system, in which the method according to the invention can be performed, either in the presence of a pump or in the presence of such a system. The SCR supply system 100 includes a pump or delivery pump 210 having a pump chamber 220, two actively controllable valves 221 and 222 for the pump chamber 220, and a filter 230. These components together form a delivery unit 200, which may be provided, for example, as a structural unit.

[0040] In the normal conveying direction, valve 221 serves as an inlet valve, while valve 222 serves as an outlet valve. Additionally, pump 210 has a conveying element 225 to increase and decrease the volume of pump chamber 220. The conveying element 225 can be, for example, a diaphragm, as will be explained in more detail below.

[0041] Pump 210 is now configured to deliver reducing agent 121 (or reducing agent solution) as the fluid to be delivered from fluid tank 120 via pressure line 122 to metering module or metering valve 130. The reducing agent 121 is then injected there into the exhaust gas line 170 of the internal combustion engine.

[0042] In addition, a pressure sensor 140 (which may also be housed in the delivery unit 200) is provided, which is configured to measure the pressure at least in the pressure pipe 122. A computing unit 150, configured as an exhaust aftertreatment controller, is connected to the pressure sensor 140 and obtains information about the pressure in the pressure pipe 122 from it. Furthermore, the exhaust aftertreatment controller 150 is connected to the delivery unit 200, specifically to the pump 210, and to the metering module 130, so that it can be controlled. This also includes the control of the actively controllable valves 221 and 222.

[0043] Additionally, the SCR supply system 100 includes, for example, a return line 160 through which the reducing agent can be returned from the system to the fluid storage tank 120. An orifice or throttling section 161 is provided in the return line 160, for example, to provide localized flow resistance. However, it should be noted that this return line can be omitted in the case of a pump with an actively controlled valve.

[0044] The exhaust aftertreatment controller is configured to coordinate the system's actuators based on relevant data, such as data received from the motor controller or from sensors monitoring temperature, pressure, and nitrogen oxide content in the exhaust gas, to introduce an aqueous urea solution upstream of the SCR catalyst into the exhaust duct according to the operating strategy. Additionally, on-board diagnostics (OBD) monitors components and parts of the exhaust aftertreatment system related to maintaining exhaust gas limits, for example.

[0045] exist Figure 2 China and Belgium in Figure 1 Pump 210 is shown schematically in cross-sectional view in more detail, in which the method according to the invention can be implemented. In addition to pump chamber 220 and two actively controllable valves 221 and 222 for pump chamber 220, pump 210 has in particular an element 225 configured as a diaphragm that defines pump chamber 220.

[0046] In addition, an electric motor 240 is provided, with its rotor 245, for example by means of an eccentric wheel (see angle for this). A connecting rod 250 is mounted, which 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 250.

[0047] Here, the two valves 221 and 222 have, for example, electromagnetic actuators, each having a coil 223 and an armature 224. By means of the electromagnetic actuators, suitable elements can be operated to release flow, i.e., to open or block the valve, i.e., to close the valve.

[0048] exist Figure 3 The diagram illustrates the following based on Figure 2The pump control process can also be used within the framework of the method according to the invention. For this purpose, a graph is plotted with respect to time t or angle. (In the case of an electric motor rotor) the pump stroke h (e.g., piston stroke or diaphragm stroke). Here, the stroke h varies between top dead center OT and bottom dead center UT, where the pump chamber has its maximum volume at OT and its minimum volume at UT. Curve V1 here describes the fluid transport from tank 121 to pressure line 122.

[0049] Now, curve V1 shows the fluid delivery 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, where a valve is actuated (opened or closed).

[0050] For better understanding, these two valves will be referred to as the inlet valve and the outlet valve, respectively. Fluid flows into the pump chamber through the inlet valve and then flows out through the outlet valve. Normal delivery and return delivery are carried out in the same manner, wherein, in the case of delivery, the inlet valve (221) is positioned on the fluid storage tank side and the outlet valve (222) is positioned on the dispensing module side. In the case of return delivery, this is exactly the opposite.

[0051] At point A, the pump chamber is filled with fluid (having at least substantially the maximum volume). Outlet valve 222 is initially closed but is opened at point A. Inlet valve 221 is and remains closed. This allows fluid to be delivered out of the pump chamber.

[0052] Then at point B, the fluid is at least substantially completely (complete evacuation is impossible in practice) expelled from the pump chamber. Then outlet valve 222 is closed. Immediately thereafter, or at most for a very short time, the initially closed inlet valve 221 is opened at point C, while the outlet valve remains closed.

[0053] This draws fluid into the pump chamber in the direction of OT during the subsequent stroke. Upon reaching OT, inlet valve 221 is closed at point D, and the pump chamber is filled with fluid. This process is then repeated starting from point A.

[0054] As mentioned earlier, when using actively controllable valves (see...) Figure 2 In such cases, it is necessary to manipulate or energize the coil of the corresponding electromagnetic actuator used in the valve as specifically as possible in order to open or close the valve at critical or desired times.

[0055] Figures 4 to 6 The diagram illustrates graphs of exemplary current curves for controlling a valve in the method according to the invention, in different preferred embodiments. Current I is plotted for this purpose with respect to time t, the current at the valve (see...). Figure 2The current flows within the coil. Figure 6 Additional land such as in Figure 3 The pump stroke h was plotted with respect to time t, as shown in the diagram.

[0056] exist Figure 4 The diagram above illustrates a variation in which, initially at the start of activation, during the attraction phase P... A A voltage is applied to the coil until a first current intensity I1 is reached. In this case, the valve is continuously energized until movement of the valve mechanism is detected.

[0057] After identifying the complete motion, in the post-attraction phase P N The coil is still energized, especially only briefly, to ensure that the armature of the valve is firmly held in its seat and does not spring back.

[0058] Then, stop energizing the coil, and during the shutdown phase P S The coil energy is unloaded or the current is reduced by using a freewheeling circuit or a freewheeling diode. In this case, the unloading curve will show an armature drop in current, i.e., a brief increase in current shortly before the curve ends. This parameter can be used in control strategies to identify the actual shutdown point.

[0059] Rapid quenching is not used in this variant; however, as has been demonstrated, it is only possible or meaningful if there is sufficient time to close the valve, since closing the valve via the freewheeling circuit requires a relatively long time. However, a reduced armature sound occurs as the armature falls back into its seat, and a smaller mechanical load is also generated by the slow armature movement.

[0060] The intermediate chart shows a variation that, compared to the variation based on the chart above, occurs in the post-attraction phase P. N Afterwards and during the closing phase P S In this circuit, when the valve is de-energized, the coil energy is unloaded in the first part through a freewheeling circuit, as indicated by F. Using this method, the freewheeling circuit or freewheeling diode absorbs part of the power loss, which is converted into heat (power loss) in the control electronics during the quenching process.

[0061] However, most of the stored coil energy is extracted from the coil through rapid quenching, as indicated by the "S". A follow current is then used again before the mechanical armature movement begins to reduce noise as the armature falls back into its seat and to achieve a smaller mechanical load through slow armature movement.

[0062] Alternatively, the remaining energy can be extracted from the coil by rapid quenching (see the rightmost step) at the end of the armature movement. This way, only the time range within the armature movement is operated using a freewheeling circuit, while the range before and after is operated using rapid quenching.

[0063] This allows for a good analysis of the current characteristics of the armature falling back, so that the software can continue processing at that point in time.

[0064] The diagram below shows a variation, compared to the variation based on the intermediate diagram, in the post-attraction phase P N Afterwards and during the closing phase P S In this process, when the valve is de-energized, the coil energy is immediately unloaded via the freewheeling circuit (marked with F). Using this method, the freewheeling circuit or freewheeling diode absorbs some of the power loss, which is converted into power loss in the control electronics during the quenching process. The coil energy is then completely unloaded through a rapid quenching phase, marked with S.

[0065] The advantage of this variant is that the operation time is exceptionally short and even smaller tolerances are achieved when the valve is closed. In particular, the use of the fast-quenching variant, as shown in the middle and lower diagrams, allows for the rational use of actively controllable valves at high speeds of the pump's electric motor, which requires exceptionally short valve opening times.

[0066] exist Figure 5 The above chart shows a variant, which is based on Figure 4 Compared to the variant, P in the post-attraction stage N Afterwards and during the closing phase P S In the holding phase, when the energizing supply to the valve is stopped, the valve continues to remain open (attractive) with a reduced current. Therefore, during the holding phase, P... H The average (effective) setting is a second current intensity I2 that is less than the first current intensity I1.

[0067] As can also be clearly seen, this is preferably achieved by means of PWM control (i.e., pulse width modulation control). However, the second current intensity is preferably higher than the minimum current intensity required to keep the valve open. A conclusion regarding the coil temperature can also be drawn from this, as mentioned earlier.

[0068] During the maintenance phase P H Then comes the closing phase P. S In this stage, the method of valve closure can preferably be selected. This can be achieved by means of rapid quenching or follow-through (as indicated here by S and F), but also by other combinations or just one of them. In particular, in this case, it can be... Figure 4 The different variations shown are used for closing phase P S. Figure 5 The alternation between rapid quenching, follow-through, and rapid quenching again at the end is shown.

[0069] The diagram above shows a variation in which the holding phase begins immediately after the post-attraction phase, while in the variation shown in the diagram below, the current is reduced by means of the freewheeling F before the holding phase begins.

[0070] Figure 5 The variation shown allows for a longer valve opening duration without causing excessive coil heating. Therefore, the actively controllable valve can also be reasonably used for low-speed applications with the pump's electric motor.

[0071] In this respect, the use of freewheeling according to the following diagram has the following advantages, for example: the current drops to the holding current level (or the second current intensity I2) more quickly and in a targeted manner.

[0072] By controlling pulse width modulation during the holding phase, the valve opening can be adapted so that the opening behavior over time matches the rotational speed and the required throughput of the fluid to be transported.

[0073] exist Figure 6 (using according to) Figure 3 The terminology indicates the opening (at point A) and closing (at point B) of an actively controllable valve, along with the associated coordinated current curves for energizing the coil.

[0074] The left side shows the longer opening duration required to open at low speeds, while the right side shows the shorter opening duration required to open at high speeds. In both cases, the method described is exemplarily applied according to... Figure 5 The curves in the chart above have corresponding holding phases of different durations.

Claims

1. A method for operating a pump (210), the pump having a pump chamber (220), two valves (221, 222) for the pump chamber (220), wherein at least one valve has an electromagnetic actuator including a coil (223) and an armature (224) and is therefore actively controllable, the pump also having an electric motor (240) by means of which an element (225) limiting the pump chamber (220) can be reciprocated. in, During the attraction phase (P A In order to open at least one actively controllable valve, the valve coil is energized until at least a first current intensity (I1) is reached. During the shutdown phase (P) S The current in the coil is reduced, thereby closing the valve; and In the attraction phase (P) A ) and closing phase (P S Between the two phases, during the maintenance phase (P) H In this process, a second current intensity (I2) less than the first current intensity is applied to the coil to keep the valve open, and This involves, at least temporarily, using rapid quenching to reduce the current in the coil. In this method, the current in the coil is passively reduced by means of a idling diode. In the post-attraction phase (P) N After that and during the closing phase (P) S In this process, when the valve is de-energized, the coil energy is unloaded in the first part through the freewheeling circuit. Most of the stored coil energy is extracted from the coil through rapid quenching, and then the follow current is used again before the mechanical armature movement begins.

2. The method according to claim 1, wherein, If the electric motor speed is below the first threshold, then the holding phase (P) is used. H Furthermore, if the rotational speed of the electric motor is higher than a second threshold, which is greater than or corresponds to the first threshold, the current in the coil is reduced at least temporarily by means of rapid quenching (S).

3. The method according to claim 1 or 2, wherein, During the maintenance phase (P) H In this process, PWM control is used to energize the coil at a second current intensity on an even basis.

4. The method according to claim 1 or 2, wherein, After reaching the end position of the armature, continue to energize the coil to prevent the armature from being pulled back during the later attraction phase (P). N (The rebound occurred.) 5. The method according to claim 1 or 2, wherein, During the attraction phase (P A ) and maintenance phase (P H The current in the coil will be reduced to a second current intensity by freewheeling (F) between the two currents.

6. The method according to claim 1 or 2, wherein, During the attraction phase (P A At least temporarily, PWM control is used to energize the coil.

7. The method according to claim 1 or 2, wherein, During the maintenance phase (P) H Temperature measurements of the coil are performed during this period.

8. The method according to claim 1 or 2, wherein, Fluid (121) is delivered in the SCR supply system (100) by means of a pump.

9. A computing unit (150) configured to implement all method steps of the method according to any one of claims 1 to 8.

10. A computer program product comprising a computer program that, when executed on a computing unit (150), causes the computing unit (150) to perform all the method steps of the method according to any one of claims 1 to 8.

11. A machine-readable storage medium having a computer program according to claim 10 stored thereon.

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