Method and control for operating a dosing module

Abstract

Method for operating a metering module (10) for metering a liquid with a pumping device driven by a magnetic coil (12), wherein liquid is supplied to the pumping device under a supply pressure, wherein the pumping device compresses the liquid in a pumping chamber (15) to a working pressure, and wherein a valve device closes the pumping chamber (15) with spring force and opens it to a working chamber at a predetermined working pressure by means of a stop-free, externally opening nozzle needle (16), characterized in that the magnetic coil (12) is supplied with an electrical voltage profile with at least two phases of high voltage followed by a low voltage and then a rapid extinguishing (29) with reverse polarity.

Description

State of the art

[0001] The invention relates to a method for operating a metering module for metering a liquid with a pump device driven by a magnetic coil, wherein liquid is supplied to the pump device under a supply pressure, wherein the pump device compresses the liquid in a pump chamber to a working pressure, and wherein a valve device closes the pump chamber with spring force and opens it to a working chamber at a predetermined working pressure by means of a stop-free, externally opening nozzle needle.

[0002] The invention further relates to a control system for operating a metering module for metering a liquid with a pump device driven by a magnetic coil, wherein liquid is supplied to the pump device under a supply pressure, wherein the pump device is provided for compressing the liquid in a pump chamber to a working pressure, and wherein a valve device is provided for closing the pump chamber with spring force and for opening it at a predetermined working pressure by means of a stop-free, externally opening nozzle needle towards a working chamber.

[0003] To reduce pollutant emissions, it is known to inject liquids, particularly reducing agents, into the exhaust system of internal combustion engines. For example, nitrogen oxide emissions from combustion engines can be reduced by exhaust aftertreatment using selective catalytic reduction (SCR). In this process, a defined quantity of a selectively acting reducing agent is added to the exhaust gas. Ammonia can be used as an example, which is obtained from a precursor substance in the form of urea or from a urea-water solution (HWH). To obtain ammonia from the urea-water solution, it is injected into the exhaust system upstream of an SCR catalyst.

[0004] In DE 10 2007 029 674 A1, such an exhaust gas purification system for an internal combustion engine is described, in which the NO is reduced. xFor emissions control, an SCR catalyst is used, which reduces the nitrogen oxides contained in the exhaust gas to nitrogen using the reagent ammonia. The ammonia is obtained from the hydrogen peroxide (HPM) in a hydrolysis catalyst located upstream of the SCR catalyst. The hydrolysis catalyst converts the urea contained in the HPM to ammonia and carbon dioxide. In a second step, the ammonia reduces the nitrogen oxides to nitrogen, producing water as a byproduct. The exact process has been sufficiently described in the technical literature (see WEISSWELLER in CIT (72), pages 441-449, 2000). The HPM is supplied in a reagent tank and is known, for example, as AdBlue in a 32.5% solution.

[0005] The reducing agent is injected into the exhaust manifold via a metering module and atomized as finely as possible. Furthermore, for the regeneration of particulate filters, fuel is metered into the exhaust manifold upstream of the particulate filter and atomized to increase the exhaust gas temperature and promote the combustion of the accumulated soot particles. Here, too, fine atomization is essential. This can be achieved by sufficient pressure in the liquid during injection and by a small gap at the nozzle opening between the nozzle needle seat and the nozzle needle itself. At high liquid pressure, the nozzle needle is accelerated significantly and performs a movement with an undesirably large stroke unless this is limited to the desired value in the range of a few hundred micrometers by a stroke stop. Such a stroke stop must be precisely adjusted during manufacturing, which incurs additional costs.

[0006] Furthermore, the forces acting on the nozzle needle during acceleration and deceleration are associated with undesirably high noise levels. If the dosing module is used to meter a urea-water solution for the selective catalytic reduction (SCR) of nitrogen oxides, the urea-water solution can freeze in the dosing module at low temperatures. In a system with a stroke stop, this stop can freeze, and the ice pressure in the sealed channel volume can increase to such an extent that the ice pressure resistance of the dosing module is compromised.

[0007] DE 198 54 508 C1 describes a metering device comprising a housing with an actuator mounted therein, a fluid chamber pressurizable with a fluid, at least one injection port connected to the fluid chamber through which the fluid can be discharged from the fluid chamber to the outside, a valve needle driven by the actuator which extends through the fluid chamber and by means of whose stroke the opening and closing of the injection port can be controlled, wherein the valve needle is designed to open outwards, axially pressure-acting surfaces of the valve needle and the housing are provided, which are designed such that a change in the pressure of the fluid results in the same axial change in length of the valve needle and the housing. According to the Fig. In cases 1 to 3, the outwardly opening valve has no stroke limitation.

[0008] DE 10 2008 044 144 A1 describes a method for controlling an injection characteristic of a fuel injector, the method comprising the following steps: supplying a control current to an electromagnetic actuating device of the fuel injector to actuate a valve element to open and close a nozzle orifice, wherein the supply comprises a first change of at least one current value of the control current and / or a current gradient of the control current at an initial stage of the supply corresponding to a variation of an injection time delay in each fuel injector, wherein the injection time delay is a duration from a first time at which the supply is started to a second time at which the valve element opens the nozzle orifice. Furthermore, DE 10 2008 044 144 A1 describes a fuel injection control device for carrying out the method.This is intended to reduce the injection time delay and prevent an increase in processing load. See the figures, e.g. Fig. 4, Fig. 7, Fig. 10, Fig. 11 and Fig. Figure 12 shows typical current profiles with a current peak at the beginning, corresponding to a first booster phase, and a holding phase after this booster phase.

[0009] From DE 102 30 267 A1, a method for controlling a fluid metering device with a closing device, in particular a solenoid valve for controlling the fuel metering in an internal combustion engine, is known, in which at least a first opening force that causes the opening of the closing device is varied depending on the fluid pressure applied to the fluid metering device. Furthermore, a common-rail injector with a closing device, in particular a solenoid valve with an armature, and a control device for controlling the fuel metering in an internal combustion engine is disclosed, in which an accelerating voltage of the booster capacitor serving the solenoid valve is controllable for opening the solenoid valve, and an induction current causes an opening force on the solenoid valve, in particular for carrying out the method, wherein the induction current and / or the accelerating voltage are variable depending on a rail pressure. Fig. 4, Fig. 5 and Fig. Figure 6 shows typical current and voltage waveforms with a booster phase (I), during which an increased current flows through the valve, and a subsequent holding phase (II), during which the current is reduced compared to phase I. In phase III, following phase II, the voltage across the capacitor is increased, thus reducing the injector current.

[0010] A disadvantage of the prior art is that at high injection pressure a nozzle needle with a stroke stop must be used in order to promote atomization of the liquid into small droplets by limiting the lamellar thickness of the liquid film.

[0011] It is therefore an object of the invention to provide a method which makes it possible to use a stop-free nozzle needle in a metering module for an injection pressure greater than 5 bar and to limit the opening stroke of the nozzle needle to a few hundred micrometers.

[0012] It is also an object of the invention to provide a control system suitable for carrying out the method.

[0013] From DE 100 14 228 A1, a method for controlling a fuel injection valve is known in which several booster pulses (B1, B2, ...) are activated at freely selectable times during the control phase. The multiple, freely positionable booster pulses aim at economical energy use, ensuring operation at low battery voltage, and optimizing needle movement.

[0014] From DE 10 2011 077 617 A1, a conveying unit is known in which the components of the magnetic assembly (magnetic coil, yoke) are arranged separately from the fluid-carrying components of the pump housing. The pump chamber is closed by a check valve.

[0015] From DE 10 2012 206 481 A1, a metering valve with an integrated pump is known in which the stroke of a hollow-drilled piston is precisely limited by fixed mechanical stops (magnetic sleeve, stop sleeve). This establishes a defined delivery volume per stroke and improves metering accuracy. Disclosure of the invention

[0016] The problem relating to the method of the invention is solved by supplying the magnetic coil with an electrical voltage profile consisting of at least two phases of high voltage followed by a subsequent low voltage, and then a rapid quenching with reversed polarity. To generate pressure, the magnetic coil is energized so that an actuator moved by the magnetic field pressurizes the liquid to be metered via a diaphragm in a pump chamber connected to the diaphragm. Once the pressure is sufficiently high, a nozzle needle or valve needle moves outwards towards the working chamber and opens the access to the pump chamber at a nozzle seat or valve seat, allowing the liquid to exit into the working chamber. The gap between the nozzle seat and the nozzle needle must remain small enough to achieve fine atomization of the liquid with a desired droplet size distribution.

[0017] If, according to the prior art, the magnetic coil is subjected to an electrical voltage profile with an initial high-voltage phase (booster phase), followed by a low-voltage phase (hold phase), and then a rapid extinguishing with reversed polarity, the end-stop nozzle needle is accelerated so strongly that it achieves an undesirably large stroke height of, for example, 0.5 mm, thereby undesirably increasing the droplet size to a diameter greater than 100 micrometers. If an end-stop nozzle needle is used in a metering module, the operating pressure is also limited to a range below 3 bar when controlled according to the prior art, as occurs, for example, in a system for metering diesel fuel into the exhaust manifold of an internal combustion engine for the regeneration of a diesel particulate filter. Such a metering module is used as a Diesel Injection Valve (DIV) in a Departronic system from Bosch GmbH.

[0018] Furthermore, the strong acceleration and, when using a nozzle needle with a stop, its deceleration at the stop, generate undesirably loud noises. By dividing the voltage curve according to the invention into at least two booster phases, each followed by holding phases, the acceleration of the nozzle or valve needle is reduced, thus lowering the noise generation and the stroke height. Due to the smaller gap between the nozzle seat and the nozzle needle, on the order of a few hundred micrometers, typically 250 micrometers, the resulting lamellar thickness of the liquid film is less than in the prior art, thus promoting its disintegration into small droplets.

[0019] A particularly easy-to-implement variant of the method provides that the duration of the first high-voltage phase and / or the first low-voltage phase and / or the second high-voltage phase and / or the second low-voltage phase is defined in a characteristic curve as a function of the temperature of the dosing module and the supply pressure.

[0020] One variant of the method, using a pressure sensor to determine the pressure profile in the pump chamber, provides that the first high-voltage phase is terminated when the operating pressure exceeds a predetermined multiple of the supply pressure, particularly when the operating pressure exceeds 1.2 times the supply pressure. The first high-voltage phase serves to build up the pressure in the pump chamber sufficiently quickly. This also ensures that injection occurs as soon as possible after the solenoid coil is activated. According to the invention, when the pressure in the pump chamber rises noticeably, the electrical voltage at the solenoid coil is reduced to such an extent that, in the subsequent low-voltage holding phase, further pressure build-up can occur while the nozzle needle is still on the nozzle seat, i.e., while the metering valve is still closed.Due to the reduced pressure increase, the accelerating force on the nozzle needle is lower, and during the subsequent opening phase, its stroke oscillates less than with a control system according to the state of the art.

[0021] When the nozzle needle detaches from the nozzle seat and the valve assembly of the metering device opens, the rate of pressure rise in the pump chamber decreases. Therefore, to maintain sufficient pressure in the pump chamber, the first low-voltage phase (first holding phase) is terminated and the second high-voltage phase (second booster phase) is initiated when the pressure curve in the pump chamber reaches an inflection point during the first low-voltage phase and the rate of pressure rise slows.

[0022] During the second high-voltage phase at the magnetic coil, the operating pressure in the pump chamber is increased to achieve fine atomization with small droplet size. Once this is sufficiently achieved, the electrical voltage can be reduced back to the holding voltage to prevent excessive acceleration of the nozzle needle. According to the invention, the second high-voltage phase is therefore terminated and the second low-voltage phase begins when the pressure curve in the pump chamber reaches an inflection point during the second high-voltage phase and the rate of increase in the pressure curve becomes steeper.

[0023] The problem relating to the control system of the invention is solved by the control system comprising a circuit or program sequence for supplying the magnetic coil with an electrical voltage profile consisting of at least two phases of high voltage followed by a subsequent low voltage, and then a rapid extinguishing phase with reversed polarity. To reduce the acceleration of the nozzle needle, and thus to reduce its maximum stroke, it can be provided that several phases of high voltage at the magnetic coil with a high pressure rise in the pump chamber alternate with holding phases of low voltage.

[0024] The process and control system are particularly suitable for use in a system for metering fuel for the regeneration of a particulate filter or a reagent for selective catalytic reduction into the exhaust manifold of an internal combustion engine. By reducing the stroke of the nozzle needle, the gap between the nozzle seat and the nozzle needle can be kept small, thus reducing the thickness of the liquid film during injection into the exhaust manifold. This improves the atomization of the diesel fuel or the urea-water solution (AdBlue). Improving atomization by increasing the operating pressure would require more energy and therefore higher costs. The reduction in noise associated with the shorter stroke of the externally opening nozzle needle has a positive effect on the system's acceptance.If a stop were provided to limit the size of the gap between the nozzle needle seat and the nozzle needle itself, this stop would have to be individually and laboriously adjusted during manufacturing. This would result in an increase in the cost of the metering module.

[0025] The invention will be explained in more detail below with reference to an embodiment illustrated in the figures. The figures show: Fig. 1 a dosing module in sectional view, Fig. 2 a first stress-time diagram, Fig. 3 a first hub-time diagram, Fig. 4 a second voltage-time diagram, Fig. 5 a second hub-time diagram, Fig. 6 a pressure diagram, Fig. 7 a size distribution of drops at the outlet of the dosing module.

[0026] Fig. Figure 1 shows a sectional view of a metering module 10. The metering module 10 is housed in a casing 11. A magnetic coil 12, driven by an applied electrical voltage, is provided to drive pressure generation. This coil acts on an actuator 13, which in turn acts on a diaphragm 14. The diaphragm 14 connects to a pump chamber 15, in which the liquid to be metered can be pressurized. When the pressure is sufficiently high, a nozzle needle 16 moves outwards into a working chamber and opens the access to the pump chamber 15 at a nozzle seat 18, allowing the liquid to exit into the working chamber. The gap between the nozzle seat 18 and the nozzle needle 16 must remain small enough to achieve fine atomization of the liquid with the desired droplet size distribution. The nozzle assembly is closed by a spring 17 pressing the nozzle needle 16 into the nozzle seat 18.

[0027] Fig. Figure 2 shows the time profile of an electrical voltage applied to the magnetic coil 12 during a metering process in a first voltage-time diagram 20. A first voltage profile 22 is plotted along a first time axis 24 and a voltage axis 21. The first voltage profile 22 corresponds to the state of the art. For a metering process, the first voltage profile 22 initially specifies a high voltage of, for example, 60 volts, which is reduced to a low positive value in the range of, for example, 10 volts during a conventional holding phase 28 when the nozzle needle 16 opens at the nozzle seat 18. To close the metering module 10, a negative voltage of, for example, -50 to -60 volts is applied during a rapid extinguishing 29.

[0028] Fig. Figure 3 shows a first stroke-time diagram 30 depicting a first stroke profile 32 for the stroke of the nozzle needle 16 when the magnetic coil 12 is energized with the first voltage profile 22. The first stroke profile 32 is plotted along a second time axis 34 and a stroke axis 31. During the high-voltage phase of the first voltage profile 22, pressure builds up in the pump chamber 15, and the nozzle needle 16 is pressed into the nozzle seat 18 by the spring 17. Once the pressure is sufficiently high, the first stroke profile 32 begins to rise, and the supply voltage to the magnetic coil 12 can be reduced in the conventional holding phase 28. The force exerted on the nozzle needle 16 by the pressure in the pump chamber 15 provides it with an initial impulse, causing it to continue moving during the conventional holding phase 28, and thus the first stroke profile 32 continues to rise.After a maximum stroke of, for example, 0.5 mm, the jet needle 16 is moved back by the spring 17 and the stroke decreases. This is supported by the quick-extinguishing mechanism 29.

[0029] In the prior art arrangement shown, the high pressure of, for example, 40 bar and the rapid pressure rise in the pump chamber 15, as used in metering systems for selective catalytic reduction (SCR), lead to an undesirably long initial stroke 32. To prevent exceeding the maximum permissible valve stroke of a few hundred micrometers from a fluid mechanics perspective, a mechanical stroke limiter for the nozzle needle 16 is often provided. This limits the thickness of the liquid film generated by the metering module 10, thus promoting the fragmentation of the lamella into small droplets. However, such a stroke limiter requires a complex and therefore costly adjustment process.In contrast, outwardly opening valves without a stroke stop, as described in the present invention, are only applicable at small and constant pressures, such as 2.7 bar, as is used, for example, in a Departronic system for metering diesel fuel during a cleaning cycle of a particulate filter manufactured by Bosch GmbH.

[0030] Fig. Figure 4 shows, in a second voltage-time diagram 20A, the time profile of the electrical voltage applied to the magnetic coil 12 during a dispensing process. A second voltage profile 23 according to the invention is plotted alongside the first voltage profile 22 along the first time axis 24 and the voltage axis 21. For a dispensing process, in the second voltage profile 23, a high voltage is initially applied during a first booster phase 25, then the voltage is reduced during a first holding phase 26, and then increased again to a high voltage in a second booster phase 27. After a further holding phase, a negative voltage is applied to close the dispensing module 10 during the rapid extinguishing 29.

[0031] Fig. Figure 5 shows a second stroke-time diagram 30A, in addition to the first stroke curve 32, a second stroke curve 33 for the stroke of the nozzle needle 16 when the solenoid coil 12 is energized with the second voltage curve 23. The second stroke curve 33, like the first stroke curve 32, is plotted along the second time axis 34 and the stroke axis 31. During the first booster phase 25, pressure is built up in the pump chamber 15, and the nozzle needle 16 is pressed into the nozzle seat 18 by the spring 17. To reduce the acceleration of the nozzle needle 16, the electrical voltage at the solenoid coil 12 is reduced during the first holding phase 26. Once the pressure is sufficiently high, the second stroke curve 33 begins to rise. As soon as the slope slows, the supply voltage of the solenoid coil 12 is increased again in the second booster phase 27.Due to the reduced acceleration compared to the state of the art, the jet needle 16 only achieves a maximum stroke of 0.25mm through this control before it is moved back by the force of the spring 17 and closes the jet seat 18.

[0032] Fig. Figure 6 shows a pressure diagram 40, plotting a first pressure curve 42 and a second pressure curve 43 along a third time axis 44 and a pressure axis 41. The first pressure curve 42 is established as the working pressure in the pump chamber 15 when the solenoid coil 12 is energized with the first voltage curve 22. The second pressure curve 43 is established when the solenoid coil 12 is energized with the second voltage curve 23. If the second pressure curve 43 exceeds a predetermined pressure threshold 45, this indicates that the pressure increase begins and the first booster phase 25 can be terminated to prevent excessive acceleration of the nozzle needle 17. The pressure threshold 45 can, for example, be set to 1.2 times the supply pressure of the liquid to the metering module 10. The first holding phase 26, which now begins, serves to further increase the pressure with the valve still closed and a subsequent moderate increase in the valve stroke.The lower voltage in this phase reduces the power and lowers the force increase of the magnetic circuit. This reduces the pressure rise compared to the control with the first voltage curve 22. If a first inflection point is detected in the second pressure curve 43 during the first holding phase 26, the first holding phase 26 is terminated and the second booster phase 27 is initiated to prevent the operating pressure from dropping too low. The first inflection point in the second pressure curve 43 indicates that fluid is flowing out of the pump chamber 15 after the nozzle needle 16 opens and injection is beginning. Since a reduction in pressure would cause the droplet size to increase undesirably, the second booster phase 27 is initiated.If a second turning point occurs in the second pressure curve 43, this is an indicator of the effectiveness of the second booster phase 27, the second booster phase 27 is terminated and the voltage is reduced back to holding level.

[0033] Fig.Figure 7 shows a size diagram 50 of the drops produced by the dosing module 10, plotting a first drop size profile 52 and a second drop size profile 53 along a fourth time axis 54 and a size axis 51. The first drop size profile 52 occurs when the magnetic coil 12 is energized with the first voltage profile 22, and the second drop size profile 53 occurs when the magnetic coil 12 is energized with the second voltage profile 23. Although the first pressure profile 42 has a peak value of over 40 bar, the first drop size profile 52 shows drops of approximately 110 micrometers in size. In contrast, the second drop size profile 53, when controlled with the second voltage profile 23, shows only drops smaller than 90 micrometers.By using the second voltage curve 23 for control, a simpler and more cost-effective dosing module 10 can be used without a stop for the nozzle needle 16, which also achieves finer atomization. Due to the lower acceleration of the nozzle needle 16, such a system also operates more quietly. Furthermore, the system without a stroke stop is more robust because, when used for dosing in Selective Catalytic Reduction (SCR), freezing in a system with a stroke stop can cause the ice pressure to increase in the sealed channel volume, potentially damaging the system.

Claims

[1] Method for operating a metering module (10) for metering a liquid with a pumping device driven by a magnetic coil (12), wherein liquid is supplied to the pumping device under a supply pressure, wherein the pumping device compresses the liquid in a pumping chamber (15) to a working pressure, and wherein a valve device closes the pumping chamber (15) with spring force and opens at a predetermined working pressure by means of a stop-free, externally opening nozzle needle (16) to a working chamber, characterized by , that the magnetic coil (12) is subjected to an electrical voltage profile with at least two phases of high voltage followed by a low voltage and then a rapid extinguishing (29) with reverse polarity. [2] Method according to claim 1, characterized by, that the duration of the first phase of high voltage and / or the first phase of low voltage and / or the second phase of high voltage and / or the second phase of low voltage is determined in a characteristic map as a function of the temperature of the dosing module (10) and the supply pressure. [3] Method according to claim 1, characterized by , that the first phase of high voltage is terminated when the working pressure exceeds a predetermined multiple of the supply pressure, in particular when the working pressure exceeds 1.2 times the supply pressure. [4] Method according to claim 1 or 3, characterized by , that the first low-voltage phase ends and the second high-voltage phase begins when a pressure curve in the pump chamber (15) reaches an inflection point during the first low-voltage phase and the increase in the pressure curve decreases. [5] Method according to one of claims 1, 3 or 4, characterized by, that the second high-voltage phase ends and the second low-voltage phase begins when the pressure curve in the pump chamber (15) reaches an inflection point during the second high-voltage phase and the increase in the pressure curve increases. [6] Control for operating a metering module (10) for metering a liquid with a pump device driven by a magnetic coil (12), wherein liquid is supplied to the pump device under a supply pressure, wherein the pump device is provided for compressing the liquid in a pump chamber (15) to a working pressure, and wherein a valve device is provided for closing the pump chamber (15) with spring force and for opening at a predetermined working pressure by means of a stopless, externally opening nozzle needle (16) towards the exhaust channel, characterized by, that the control has a circuit or program sequence for applying an electrical voltage profile to the magnetic coil (12) with at least two phases of high voltage followed by a low voltage and then a rapid extinguishing (29) with reverse polarity.

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