CN112983792A

CN112983792A - Method for operating a pump

Info

Publication number: CN112983792A
Application number: CN202011441548.1A
Authority: CN
Inventors: H·克莱因克内希特; A·马茨纳; K·舍费尔
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-12-14
Filing date: 2020-12-11
Publication date: 2021-06-18
Also published as: KR20210075857A; DE102019219635A1

Abstract

The 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 comprising a coil and an armature and is thus actively controllable, and having an electric motor by means of which an element delimiting the pump chamber can be moved back and forth, wherein, in a suction phase (P)_A) In order to open at least one actively controllable valve, the coil of the valve is energized at least until a first current level (I) is reached₁) Wherein, in the off-phase (P)_S) Reducing the current in the coil, thereby closing the valve; and wherein, in the suction phase (P)_A) And a shutdown phase (P)_S) In the hold phase (P)_H) At a second current intensity (I) which is smaller than the first current intensity on average₂) The coil is energized to keep the valve open and/or wherein the current in the coil is reduced at least temporarily by means of a rapid quench (S).

Description

Method for operating a pump

Technical Field

The invention relates to a method for operating a pump of, for example, an SCR supply system, to a computing unit for carrying out the method, and to a computer program.

Background

In the aftertreatment of exhaust gases in motor vehicles, in particular for the Reduction of 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 solution into the typical oxygen-rich exhaust gas.

For this purpose, a dosing module or a dosing valve can be used, which comprises a nozzle for injecting or entraining the urea/water solution into the exhaust gas flow. Upstream of the SCR catalyst, the urea-water solution reacts to form ammonia, which in turn is combined with nitrogen oxides at the SCR catalyst, from which water and nitrogen gas are produced.

The metering valve is typically connected to the pump via a pressure line. The pump pumps the urea-water solution from the reductant tank to the dosing module. In addition, a return line, via which the excess urea-water solution can be returned, is usually connected to the reducing agent tank. An orifice or restriction in the return line may control the amount of return flow.

Disclosure of Invention

According to the invention, a method for operating a pump, a computing unit for carrying out the method and a computer program are proposed having the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description.

The invention relates to a method for operating a pump having a pump chamber with two valves for the pump chamber, wherein at least one, but suitably both, valves are actively controllable. Furthermore, an electric motor is provided, with which the element delimiting the pump chamber can be moved back and forth (or up and down). The element may preferably be a diaphragm which is coupled, for example via a connecting rod, with an eccentric wheel arranged at the rotor of the electric motor. In this case a so-called diaphragm pump, as is typically used in the SCR feed system already mentioned. In principle, the element need not necessarily be a diaphragm, but a piston can also be considered, which (directly) delimits the pump chamber. The two valves are used here in particular as inlet valve and outlet valve.

An actively controllable valve (this applies not only to inlet valves but also to outlet valves) is to be understood in this case as meaning that the opening and closing of the valve can be actively brought about in a targeted manner, to be precise by means of an electromagnetic actuator having a coil and an armature, in order to be able to switch the valve by energizing the coil. In contrast, other valves, or also valves that are frequently used in pumps in SCR systems, are valves that open passively or automatically when a certain pressure is applied. With such conventional valves, it is also possible, for example, to suck in fluid through the inlet valve into the pump chamber during the suction phase of the pump and then to force it out of the pump chamber through the outlet valve during the pumping or delivery phase, with the inlet valve closed.

A particular advantage of a pump having an actively controllable valve is that the pump can be operated in more or less arbitrary ways by individual actuation of the valve, for example also in a delivery direction opposite to the normal delivery direction. This can be the case in an SCR supply system (in which a fluid, for example a urea-water solution, is conveyed from a fluid tank to a dosing module), for example, meaning that the fluid can also be conveyed back again from the dosing module to the fluid tank, if required. For this purpose, the valves only have to be opened and closed in a corresponding manner. A conveying direction opposite to the conventional conveying direction is advantageous in particular in SCR supply systems, since there, after the internal combustion engine or diesel motor has been stopped, the fluid, for example a urea-water solution, can be returned from the dosing module into the fluid tank again in order to prevent freezing, in particular in the winter.

By specifically varying the opening and closing times of the valves, it is also possible, for example, to vary the efficiency of the pump. This has the advantage that the pump as a whole (suction-side valve, diaphragm, pressure-side valve) has particularly good dynamic properties. In this way, the pump may always operate at a non-optimal efficiency (the suction side valve and the pressure side valve are not open or closed at optimal points with respect to the operating pressure). If, for example, the higher-level control system requires a sudden change in quantity (menensprung) (increasing or in some cases also decreasing the quantity to be delivered), this can be done at the first moment by changing the efficiency of the pump system. The valve control can generally react in this respect much faster than the acceleration or deceleration of the electric motor of the pump. Thereby a much higher and more accurate dynamic adjustment of the system can be achieved. The electric motor can also be designed to be (relatively) slow (tr ä ge).

For this special operation of the pump, in general in the case of actively controllable valves, a problem can be that both valves or at least one valve do not open and close exactly in time, since this causes pressure peaks (on the pressure side). If the pressure in the pump chamber is higher than the pressure on the pressure side (the valve on the pressure side opens too late), the medium or fluid expands impulsively to the pressure side of the system and damage to the components on the pressure side (such as the pressure connection) may occur. If the valve inadvertently opens too early, the medium flows back into the pump chamber and a short-term pressure drop may occur. Similar problems occur with the suction side valves. If it opens too late, the negative pressure in the pump chamber may create a cavity, and if it opens too early, the compressed medium may be expelled from the pump chamber again towards the suction channel. If the two valves are opened overlapping, the pressure on the pressure side may be reduced towards the suction side, in an extreme case a hydraulic short-circuit occurs.

It is therefore desirable to operate actively controllable valves in a controlled and reliable manner, in which pressure fluctuations, temperature fluctuations (brought in from the outside or caused by undesired activation) or other influences such as manufacturing-induced tolerances of the valve actuator, such as internal resistance, inductivity and lift, etc., can be observed and compensated for.

Furthermore, operating conditions exist, in which (for example at high rotational speeds) the coils should be switched particularly accurately and quickly, or must be activated for a longer time. For example, at low rotational speeds of the electric motor, a longer activation time is required. In order to make the valve needle appear as neutral as possible to the superordinate control unit, it should be ensured by the representation of the current curve, by the knowledge of the current physical parameters and by skilled control that the coil always maintains its (controllable) behavior at all times even in the case of changing operating parameters (long or short opening times, temperature, voltage) and does not negatively influence the system.

The system evaluation or measurement has concluded that the control times of the individual active valves can be varied considerably depending on the rotational speed of the electric motor of the pump. Furthermore, influencing factors such as the supply voltage or the coil temperature are parameters which influence the behavior over time. The changed rotational speed already results in a different opening time in the case of a pump system of the ideal design. An opening time of, for example, approximately 30ms results at a low rotational speed (for example, approximately 500U/min) and an opening time of, for example, approximately 7.5ms results at a higher rotational speed (for example, approximately 2000U/min).

If the system is operating at or at a low operating voltage, the current on the coil rises relatively slowly and the valve opens late, and at a high operating voltage the current on the coil rises relatively quickly and the valve opens early. In which case a certain linearity can be assumed. The double voltage (for a constant time) corresponds, for example, to approximately double the current. This in turn means that approximately (in erster N ä herung) reaches the switching point at roughly twice the speed (energy applied in the magnetic field, which is sufficient to apply a magnetic force to move the armature in the valve). Since the supply voltage is usually between 10V and 30V, it is particularly important to calculate the time from the start of the energization until the mechanical movement of the valve or its armature.

In addition, the (electrical) internal resistance of the coil has a high influence. The internal resistance of the coil wire changes with temperature. Additionally, there is the fact that activation of the active valve causes heating of the coil wire. If the coil is activated often or for a long time or at a high switching voltage, it heats up and thus changes the current rise curve. The time between the start of energization and the movement of the armature is also lengthened. The same output occurs as at the start of the energization if the energy stored in the active valve or its coil at the end of the energization has to be removed or eliminated again.

If the energy potential is high at the switch-off time, it takes longer until the energy stored in the magnetic field is reduced to such an extent that the magnetic field of the coil is small enough for the armature of the valve to fall back into its valve seat again. The temperature of the coil (and its internal resistance) also play a non-negligible role, as do the voltages in the quenching circuit (L-fostcher).

In addition, it is particularly difficult to design the coil over a large voltage range associated with the current (indirectly also with the magnetic force). Its performance (rapid triggering on power up) and the magnetic force that is used to apply the force to enable the armature to move must be explored. In order to operate the coil even at low operating voltages, the coil is usually designed to have a very low electrical resistance, which in turn is disadvantageous at high operating voltages, i.e. particularly high currents, since the coil goes into its magnetic saturation.

Analysis or measurement of different operating voltages and different rotational speeds with a pump having an actively controllable valve and with a conventional coil current supply which ends at the beginning of the armature movement has shown that the minimum possible opening duration of the valve-although the current supply is switched off as early as possible and the current in the coil is optionally reduced by means of a free-wheeling circuit (freelaufcultung) or rapid quenching (Schnelll microshung) -can be longer than the actual ideal or optimal opening duration at high rotational speeds.

At low rotational speeds, a desired or optimum opening duration can be achieved, which is correspondingly longer than at high rotational speeds. Yet another problem arises here. The coil will enter magnetic saturation in case of a longer time to operate the valve (the optimum opening duration is about 30ms in case of e.g. about 500U/min). This results in a current which is limited only by the ohmic resistance of the coil. In the typical design of the coil, this leads to comparatively high power losses, which can lead to excessive heating of the coil, so that valve damage (enamelled copper wires, coil bodies, elastomers, thermoplastics, etc.) can occur. Furthermore, for example, diodes used in the control electronics for rapid quenching also generate heat to a greater extent, since they also start from this energy level with an energy discharge. Likewise, the corresponding output stage that supplies the current may also be damaged.

In the proposed method, the coil is now energized at least until a first current level is reached in an attraction phase for opening the at least one actively controllable valve. In particular, the coil is energized during the attraction phase until the end position of the armature is reached. The current in the coil is reduced during the closing phase, thereby closing the valve. Furthermore, the coil is energized in the holding phase between the attraction phase and the closing phase, on average, with a second current intensity which is smaller than the first current intensity, in order to keep the valve open, and/or the current in the coil is reduced at least temporarily by means of a rapid quenching, i.e. a voltage which is polarized opposite to the attraction phase.

In this way, the actively controllable valve can be operated independently of the rotational speed, so that on the one hand no damage due to overheating occurs, i.e. if the holding phase is used with a lower current than usual, and on the other hand a short opening time is also achieved by rapid quenching. In this connection, it is also particularly expedient to use the holding phase when the rotational speed of the electric motor is below a first threshold value, for example 1.000U/min, preferably 750U/min, and to reduce the current in the coil at least temporarily by means of rapid quenching when the rotational speed of the electric motor is above a second threshold value, which is greater than or corresponds to the first threshold value. It goes without saying that other variants can also be used in addition in the respective rotational speed range.

The first point in time of the current supply, i.e. the start phase or the attraction phase (Anzugsphase), should be charged unhindered so that the current required to move the armature is reached as quickly as possible. This is achieved in particular by identifying when the armature is moving. This can be recognized, for example, by means of a sensor or acoustically. However, it is also conceivable to (continuously) detect or measure the current for this purpose. Armature motion typically begins from the point in time when the curve deviates from the e-function (exponential function). Once the curve again follows the e-function, the armature is stopped. After reaching the end position of the armature (for example after a stop or after the end of the movement), the energization (nachbestomt) is preferably still replenished for a short time in order to avoid armature bounce (or fall back). This time is also called the post-suction phase (Nach-Anzugsphase) and is between the suction phase and the holding phase.

From this point onwards, the energization is expediently (temporarily) terminated, since the valve is in the stop and no longer energization is necessary. In this short period, the current in the coil is reduced, for example, by means of a freewheeling circuit, in particular to a second current level (then a so-called freewheeling phase), after which the valve actuation device (if provided) is switched into the holding phase. In the holding phase, the coil is particularly preferably energized with the second current intensity effectively or on average by means of PWM control. The holding phase ensures that the valve is held open at a (predefined) holding current, i.e. a second current level. But it is also entirely possible to immediately switch into the hold phase.

Thereafter, the valve (if set) is closed by rapid quenching. Alternatively or additionally, it is also possible to passively reduce the current in the coil by means of a freewheeling diode, in particular a freewheeling diode.

Ideally, the movement of the armature or of the valve needle is detected during the closing process. If motion is detected, the actual open time can be known. This can be or be used to allow the operating software to calculate when the energization is over or should be over so that the valve actually closes at the desired point in time.

All of these functions can reduce valve heating (but suitably not exceed the required heat), still maintain the valve quickly in its function, and begin quenching energy at a known level. Quenching at a constant level has the following advantages: the stored valve coil energy (in the magnetic field of the valve) is as small as possible (maximum), so the quench time is also optimally short and the valve performance is optimally utilized.

It is also advantageous if the coil is already energized at least temporarily by means of PWM control (instead of, for example, continuous control) during the attraction phase. System evaluation shows that a dependency on the supply voltage can be avoided or at least reduced. In this way, an always-on relationship that is easy to control can be formed. The basis of this manipulation is the system voltage. The magnet of the valve is designed to a certain nominal voltage, for example 10V. In this case, the pulse width and pause width (i.e. duty cycle) fractions during the actuation can be modified such that the voltage is always set to effectively apply a 10V (according to design) voltage to the coil. In this way, the energy input (and the heating of the coil) is always constant, as is the basic behavior over time in the armature movement and current behavior of the armature stop. If the valve is operated at 20V, a 50% duty cycle may approximately halve the valve voltage. In order to achieve an improvement in the continuity of this effective valve coil voltage, it is expedient to monitor the voltage within the system during valve actuation and to track the duty cycle accordingly when changes occur.

It is also possible to implement PWM control with a fixed control frequency and a variable duty cycle. Instead, variable control frequencies can also be used, for example a fixed pulse width and a variable pause width, or a variable pulse width and a fixed pause width.

In the case of the hold phase, in particular with the PWM control described above, it is also preferred to carry out a temperature measurement of the coil. The current can be measured at a specific point in time, for example during the holding phase, at which point the holding current tends to stabilize. The resistance can then be calculated from this current and the voltage applied to the coil (reduced by PWM control). With this resistance, the temperature or the temperature change can be determined based on the reference temperature according to the formula for the copper temperature coefficient. Such temperature measurements may be used to change control strategies or to check the confidence level of other system temperatures. It can also be used to completely interrupt the actuation in the event of a temperature increase in order to cool the valve again.

The computing unit according to the invention, for example a control unit of a motor vehicle, such as a motor controller or an exhaust gas aftertreatment controller or a pump controller, for example a control and/or regulating unit of an electric motor of a pump, is provided in particular in terms of programming for carrying out the method according to the invention.

The implementation of the method according to the invention in the form of a computer program or a computer program product with program code for executing all method steps is also advantageous, since this results in particularly low costs, in particular if the control device for executing is also used for other tasks and is therefore already present. Suitable data carriers for supplying the computer program are in particular magnetic, optical and electrical memories, such as hard disks, flash memories, EEPROMs, DVDs etc. Program downloads via a computer network (internet, ethernet, etc.) are also possible.

Further advantages and embodiments of the invention emerge from the description and the drawing.

Drawings

The invention is illustrated schematically by means of embodiments in the drawings and will be described below with reference to the drawings.

Fig. 1 schematically shows a fluid supply system with a pump, in the case of which a method according to the invention can be implemented.

Fig. 2 schematically shows a pump, in the case of which the method according to the invention can be implemented.

Fig. 3 schematically shows a control sequence of the pump according to fig. 2.

Fig. 4 to 6 show diagrams with current profiles for actuating a valve in the case of the method according to the invention in various preferred embodiments.

Detailed Description

Fig. 1 shows schematically and exemplarily a fluid supply system 100 designed as an SCR supply system, in the case of which or in the case of which a pump is present, the method according to the invention can be carried out. The SCR feeding system 100 comprises a pump or delivery pump 210 having a pump chamber 220, two actively

controllable valves

221 and 222 for the pump chamber 220 and having a filter 230. These components together form a conveying unit 200, which may be provided, for example, as a structural unit.

In the normal conveying direction, valve 221 serves as an inlet valve, while valve 222 serves on the contrary as an outlet valve. In addition, the pump 210 has a delivery member 225 to increase and decrease the volume of the pump chamber 220. The transport element 225 may be, for example, a septum, as will be explained in more detail below.

The pump 210 is now provided for delivering the reducing agent 121 (or reducing agent solution) as a fluid to be delivered from the tank 120 to the metering module or metering valve 130 via the pressure line 122. Where the reducing agent 121 is then injected into the exhaust line 170 of the internal combustion engine.

Furthermore, a pressure sensor 140 (which may also be arranged in the delivery unit 200) is provided, which is provided for measuring the pressure at least in the pressure line 122. A computing unit 150, which is designed as an exhaust gas aftertreatment controller, for example, is connected to the pressure sensor 140 and receives information therefrom about the pressure in the pressure line 122. Furthermore, the exhaust gas aftertreatment control unit 150 is connected to the delivery unit 200, in particular to the pump 210, and to the metering module 130 in order to be able to control them. This also includes the manipulation of actively

controllable valves

221 and 222.

In addition, the SCR supply system 100 comprises, for example, a return line 160, via which the reducing agent can be guided back from the system into the fluid tank 120. In the return line 160, for example, an orifice or throttle 161 is arranged, which provides a local flow resistance. It is to be noted, however, that such a return line can also be dispensed with in the case of pumps with actively controlled valves.

The exhaust gas aftertreatment controller is provided for coordinating the actuators of the system in dependence on relevant data, for example data received from the motor controller or from sensors for temperature, pressure and nitrogen oxide content in the exhaust gas, in order to introduce an aqueous urea solution into the exhaust tract upstream of the SCR catalyst in accordance with an operating strategy. Additionally, on-board diagnostics (OBD), for example, monitor components and assemblies of the exhaust aftertreatment system associated with maintaining exhaust limits.

In fig. 2, the pump 210, in which the method according to the invention can be carried out, is schematically illustrated in a sectional view in greater detail than in fig. 1. In addition to the pump chamber 220 and the two actively

controllable valves

221 and 222 for the pump chamber 220, the pump 210 has, in particular, an element 225 designed as a diaphragm, which delimits the pump chamber 220.

Furthermore, an electric motor 240 is provided, on the rotor 245 of which an eccentric wheel (see the angle for this), for example, is used

) A connecting rod 250 is positioned, which is also connected to the diaphragm. In this manner, the up-and-down movement of the diaphragm 225 may be achieved by the rotational movement of the rotor 250.

The two

valves

221 and 222 in this case have, for example, electromagnetic actuators, each having a coil 223 and an armature 224, by means of which suitable elements can be operated to release the throughflow, i.e. to open or block the valve, i.e. to close the valve.

Fig. 3 schematically shows a control sequence of the pump according to fig. 2, which can also be used in the framework of the method according to the invention. For this purpose, the time t or the angle is plotted in a diagram

The pump stroke h (e.g. piston stroke or diaphragm stroke) (in the case of a rotor of an electric motor). The stroke h varies between a top dead center OT and a bottom dead center UT, the pump chamber having its maximum volume at OT and its minimum volume at UT. Curve V₁The transfer of fluid from the tank 121 into the pressure pipe 122 is described herein.

Now, curve V₁Fluid delivery by means of the pump is shown, wherein the position of the stroke and thus the current volume of the pump chamber, respectively, is shown with points A, B, C and D, wherein one of the valves is actuated (opened or closed).

For better understanding, these two valves will be referred to below as the inlet valve and the outlet valve, respectively, wherein fluid flows into the pump chamber through the inlet valve and out through the outlet valve. The normal delivery and return delivery take place in the same way, wherein, in the case of delivery, the inlet valve (221) is positioned on the fluid reservoir side and the outlet valve (222) is positioned on the dosing module side. This is exactly the other way round in the case of return conveyance.

At point a the pump chamber is filled with fluid (having at least substantially maximum volume). The outlet valve 222 is also initially closed, but is opened at point a. The inlet valve 221 is and remains closed. Thereby conveying fluid out of the pump chamber.

At point B the fluid is then at least substantially completely (in practice complete emptying is not possible) expelled from the pump chamber. The outlet valve 222 is then closed. Immediately thereafter, or at most for a short time, the initially closed inlet valve 221 is opened at point C, while the outlet valve remains closed.

Thereby drawing fluid into the pump chamber on a subsequent stroke in the OT direction. At point D, the inlet valve 221 is closed and the pump chamber is filled with fluid when OT is reached. The process is then repeated from point a.

As already mentioned above, in the case of actively controllable valves (see fig. 2), it is necessary to actuate or energize the coils of the respective electromagnetic actuators used in the valves as specifically as possible in order to open or close the valves at critical or desired points in time.

Fig. 4 to 6 show diagrams with exemplary current profiles for actuating the valve in the method according to the invention in various preferred embodiments. For this purpose, the current I is plotted against the time t, which current flows in the coil of the valve (see fig. 2). In fig. 6, the pump stroke h is additionally plotted as in fig. 3 with respect to the time t.

Fig. 4 shows a variant in the upper diagram, in which initially at the start of activation a suction phase P is provided_AUntil a first current intensity I is reached₁. In this case, in particular, the valve is energized until a movement of the valve mechanism is detected.

After the complete movement has been recognized, a post-suction phase P_NThe coil is still energised, in particular only briefly, to ensure that the armature of the valve is held firmly in its seat and does not rebound.

Then, the energization of the coil is stopped, and in the off phase P_SWherein the coil energy or current is unloaded or reduced by a freewheeling circuit or a freewheeling diode. In this case, it can be seen in the unloading curve that the armature return is reflected in the current, i.e. the current rises briefly shortly before the end of the curve. This parameter can be used to manipulate the strategy to identify the actual closing time point.

In this variant, rapid quenching is not used, but, as has been proven, it is only possible or sensible to close the valve when there is sufficient time, since closing the valve by means of the freewheel loop takes a relatively long time. However, a reduced armature sound occurs when the armature falls back into its seat, and a smaller mechanical load is also generated by the slow armature movement.

In the middle diagram a variant is shown, in comparison with the variant according to the upper diagram, in the post-suction phase P_NAfter and during the closing phase P_SWhen the energization of the valve is stopped, the coil energy is unloaded in a first portion through the freewheel circuit, as marked with F. With this measure, the freewheeling circuit or the freewheeling diode assumes part of the power losses, which are converted into heat (power losses) in the control electronics during the quenching process.

However, a large portion of the stored coil energy is extracted from the coil by rapid quenching, as labeled with S. The follow current is then used again before the start of the mechanical armature movement in order to reduce the rattling of the armature when it falls back into its seat and to obtain a lower mechanical load by the slow armature movement.

Alternatively, the remaining residual energy can also be extracted from the coil at the end of the armature movement by rapid quenching (see the rightmost step). In this way, only the time range within the armature movement is operated with the free-wheeling circuit, and the preceding and following ranges are operated with rapid quenching.

The current characteristic of the armature return can be analyzed very well at this point in order to continue processing this point in time in the software.

In the lower diagram, a variant is shown, in which the post-suction phase P is compared with the variant according to the middle diagram_NAfter and during the closing phase P_SWhen the energization of the valve is stopped, the coil energy is unloaded at a first moment via the freewheel circuit (marked F). With this measure, the freewheeling circuit or the freewheeling diode assumes part of the power losses, which are converted into power losses in the control electronics during the quenching process. The complete unloading of the coil energy follows by a fast quenching phase, as marked with S.

The advantage of this variant is that the actuation is particularly short and even smaller tolerances are achieved in the case of a closed valve. In particular, the variant with rapid quenching according to the middle and lower graphs allows reasonable use of actively controllable valves at high rotational speeds of the electric motor of the pump, which requires particularly short valve opening times.

In fig. 5, a variant is shown in the upper diagram, in comparison with the variant according to fig. 4, in the post-suction phase P_NAfter and during the closing phase P_SWhen the energization of the valve is stopped, the valve continues to remain open (attracted) with a reduced current. For this purpose, in the hold phase P_HSet a mean (effective) value less than the first current level I₁Second current intensity I₂。

As can also be clearly seen, this is preferably done by means of PWM manipulation (i.e. manipulation of pulse width modulation). But the second current level is preferably higher than the minimum current level required to keep the valve open. Conclusions about the coil temperature can also be drawn at this point, as already mentioned above.

In the hold phase P_HFollowed by a shutdown phase P_SIt is preferably possible to choose how to close the valve during this phase. This can be done by means of rapid quenching or follow-up (as here labeled with S and F), but also by other combinations or only one of themAnd once the process is carried out. In this case, in particular, the different variants shown in fig. 4 can be used for the closing phase P_S. Fig. 5 shows the alternation of quenching from fast, freewheeling and quenching again fast at the end.

The upper diagram shows a variant in which the holding phase starts immediately after the post-attraction phase, whereas in the variant shown in the lower diagram the current is reduced by means of the freewheel F before the holding phase starts.

The variation shown in fig. 5 allows for longer valve opening durations without causing excessive heating of the coil. In this way, the actively controllable valve can also be used reasonably for low rotational speeds of the electric motor of the pump.

The use of freewheeling according to the following diagram in this connection has the following advantages, for example: the current is reduced to the holding current level (or the second current intensity I) in a targeted and faster manner₂）。

By controlling the pulse width modulation in the hold phase, the opening of the valve can be adapted such that the opening behavior over time is matched to the rotational speed and the required throughput of the fluid to be conveyed.

Fig. 6 (using the terminology according to fig. 3) shows the opening (in each case at point a) and closing (in each case at point B) of the actively controllable valve and the associated current profile, which is adapted to this, for the purpose of energizing the coil.

The left side shows the longer opening duration required for opening at low rotational speeds, while the right side shows the shorter opening duration required for opening at high rotational speeds. In both cases, the curves according to the upper diagram in fig. 5 are used as an example, but with holding phases of correspondingly different time lengths.

Claims

1. Method for operating a pump (210) having a pump chamber (220), two valves (221, 222) for the pump chamber (220), at least one of which has an electromagnetic actuator comprising a coil (223) and an armature (224) and is thus actively controllable, and having an electric motor (240) with which an element (225) delimiting the pump chamber (220) can be moved back and forth,

wherein, in the suction phase (P)_A) In order to open at least one actively controllable valve, the coil of the valve is energized at least until a first current level (I) is reached₁），

Wherein, in the closing phase (P)_S) Reducing the current in the coil, thereby closing the valve; and is

Wherein, in the suction phase (P)_A) And a shutdown phase (P)_S) In the hold phase (P)_H) At a second current intensity (I) which is smaller than the first current intensity on average₂) Energizing the coil to keep the valve open, and/or

Wherein the current in the coil is reduced at least temporarily by means of a fast quench.

2. Method according to claim 1, wherein the holding phase (P) is used if the rotational speed of the electric motor is below a first threshold value_H) And wherein the current in the coil is reduced at least temporarily by means of rapid quenching (S) if the rotational speed of the electric motor is above a second threshold value, which is greater than or corresponds to the first threshold value.

3. Method according to claim 1 or 2, wherein during the holding phase (P)_H) The coil is energized with a second current intensity on average by means of PWM control.

4. Method according to any of the preceding claims, wherein the coil is continuously energized after reaching the end position of the armature to avoid the armature from a post-attraction phase (P)_N) Middle bounce.

5. Method according to any one of the preceding claims, wherein in the attraction phase (P)_A) And a hold phase (P)_H) Between, preferably between, the post-attraction phase and the holding phase, the current in the coil is reduced by a free-wheeling (F) to a second current levelAnd (4) degree.

6. Method according to any one of the preceding claims, wherein in the shutdown phase (P)_S) Wherein the current in the coil is reduced by means of a fast quench (S).

7. Method according to any one of the preceding claims, wherein in the shutdown phase (P)_S) Wherein the current in the coil is reduced by means of a freewheel (F).

8. Method according to any one of the preceding claims, wherein in the attraction phase (P)_A) At least temporarily energises the coil by means of PWM control.

9. Method according to any one of the preceding claims, wherein during the holding phase (P)_H) During which temperature measurements of the coil are made.

10. Method according to any of the preceding claims, wherein the fluid (121) is transported in the SCR feeding system (100) by means of a pump.

11. A computing unit (150) arranged for implementing all method steps of the method according to any one of the preceding claims.

12. Computer program which, when executed on a computing unit (150), causes the computing unit (150) to carry out all the method steps of the method according to any one of claims 1 to 10.

13. A machine-readable memory medium having stored thereon the computer program according to claim 12.