Method for controlling an electrostatic air filter for the interior of a motor vehicle

Abstract

Method for controlling an electric air filter for a vehicle interior of a motor vehicle, wherein a first filter layer is charged via a first voltage source with a first voltage, and that a second filter layer is charged via a second voltage source with a second voltage having a different polarity than the first voltage, wherein the two filter layers are alternately charged and discharged.

Description

[0001] The invention relates to a method for controlling an electric air filter for a vehicle interior of a motor vehicle, wherein a first filter layer is charged with a first voltage via a first voltage source, and a second filter layer is charged with a second voltage having a different polarity than the first voltage via a second voltage source, wherein the two filter layers are alternately charged and discharged.

[0002] Modern motor vehicles are equipped with a ventilation system that allows, for example, fresh air to be drawn into the vehicle interior from outside. The ventilation system can be designed as an air conditioning system, i.e., it can also include an air conditioning unit. In order to supply the cleanest possible air, a filter device is provided that separates particles contained in the air as far as possible. Combination filters are known that separate pollen, for example, and have an activated carbon layer and an anti-allergen layer. In addition, electric air filters are known that have an electrode charged with high voltage, past which the air to be cleaned flows. The electrode, which is, for example, strongly negatively charged, emits electrons that migrate to a second electrode, which is, for example, grounded. On their path, the electrons encounter gas atoms, which ionize them, i.e.When the electrons accelerate towards the second electrode hit, further electrons are split off from the gas molecules, or the electrons emitted by the first electrode attach themselves to the gas atoms. In the first case, new free electrons and positive gas ions are created, while in the second case, negatively charged gas ions are created. Positively charged gas ions attach themselves to the negatively charged first electrode, which can also be referred to as the spray grid, and are neutralized there, while the negatively charged particles, i.e. the free electrons and the negatively charged gas ions, migrate to the second electrode, attach themselves there, and are neutralized.

[0003] The first electrode is charged with a high voltage of several kV. This creates a correspondingly strong electric field towards the second electrode, within which the electrons and gas ions migrate. Since the air to be cleaned flows past the electrodes and this migration is more or less perpendicular to the direction of air flow, it can happen that charged particles also migrate out of the electrode area and settle elsewhere in the downstream area of ​​the ventilation device. This sometimes leads to static charging in the area of ​​the electrodes and in downstream areas. If, for example, the first electrode is strongly negatively charged, the surrounding area primarily becomes negatively charged. This static charging is undesirable.

[0004] EP 0 646 416 A1 discloses an air purification device comprising an electrostatic precipitator with a downstream fiber or fabric filter. The electrostatic precipitator comprises a first and a second filter layer, to which a constant voltage of different polarity in the kV range can be alternately applied via separate voltage sources. The respective adjustable durations of the voltage cycles can be different.

[0005] JP S56-81 141 A describes an electrostatic precipitator having a first and a second discharge electrode which are alternately supplied with a voltage of different polarity.

[0006] Finally, from US 2019 / 0 024 913 A1, a filter system with an electrostatic precipitator and a heat storage element is known, which is exposed to the passing air flow.

[0007] The invention is therefore based on the problem of providing a correspondingly improved method for controlling an electric air filter.

[0008] To solve the problem, according to the invention, a method for controlling an electrostatic filter for a vehicle interior of a motor vehicle is provided, which is characterized in that the first voltage is given as a first sinusoidal voltage or first trapezoidal voltage and the second voltage is given as a second sinusoidal voltage or second trapezoidal voltage, wherein the sinusoidal voltages or trapezoidal voltages are given offset from one another in such a way that the second sinusoidal voltage or second trapezoidal voltage passes through its maximum when the first sinusoidal voltage or first trapezoidal voltage passes through its minimum.

[0009] The electric air filter used has two separate filter layers, which can be designed, for example, in the form of conductive metal mesh and / or metal needles. Each filter layer is subjected to a high voltage via a separate voltage source, with the two high voltages having different polarities, i.e., different signs. If, for example, the first filter layer is strongly negatively charged, the second filter layer will be positively charged.

[0010] The first filter layer is the filter layer through which the actual ionization process takes place, which purifies the air, as described in the introduction. It is therefore the actual "cleaning electrode." The second filter layer, on the other hand, is essentially a "neutralization electrode." It is operated alternately with the first filter layer, i.e. when the first filter layer, i.e. the first electrode, is or has been discharged. The first filter layer then no longer emits electrons. Instead, the second filter layer is highly charged, in this example, strongly positively charged, so that a large number of positively charged particles form in the area around the filter layer. These particles migrate to the first filter layer on the one hand, but also attach themselves to corresponding surfaces in the area around the electrode arrangement or arrangement of filter layers and neutralize the negative charges present there, thus neutralizing any static charges.The second filter layer, which is operated in alternation with the first filter layer, causes a targeted discharge of statically charged environmental areas at defined times through the emission of oppositely charged particles, so that the static charge can be reduced.

[0011] Different variants are conceivable with regard to the specific control. For example, according to an embodiment not according to the invention, the first voltage source can charge the first filter layer using a constant first voltage that is applied during a first time interval, while the second voltage source can charge the second filter layer using a constant second voltage that is applied during a second time interval that follows the first time interval. Constant, equal voltages in the range of several kV are therefore applied to the first and second filter layers, but at different times or over different time intervals. During regular cleaning operation, the first filter layer is operated; for example, a constant high voltage in the range of several kV is applied to it over a first time interval, for example for 5 minutes.After the time interval has elapsed, the first filter layer is discharged, the voltage drops to zero, while the second filter layer is positively charged, also with a corresponding high voltage in the range of several kV. This voltage is applied for a second time interval, lasting, for example, 1 minute. After this time interval has elapsed, the voltage is reduced again and the first filter layer is recharged. Thus, an intermittent alternation takes place.

[0012] In this embodiment, the first time interval is preferably longer than the second time interval. As described, the actual cleaning effect occurs via the first filter layer, while the neutralization or discharge occurs via the second filter layer. It is sufficient to carry out the neutralization or discharge over a shorter period of time, since the static charge develops quite slowly and does not become excessively high when the method according to the invention is carried out continuously, so that the electric air cleaner can operate in cleaning mode most of the time. The first time interval should be between 2 and 10 minutes, and the second time interval between 0.5 and 2 minutes.

[0013] According to an alternative control variant not according to the invention, the first voltage source can apply first voltage pulses to the first filter layer and the second voltage source can apply second voltage pulses to the second filter layer, the first and second voltage pulses being applied with a time offset. In this case, true pulsed operation takes place in that there is a permanent change in the operation of the first and second filter layers. The voltage pulses are only applied for a few seconds, i.e. there is a higher frequency change between the charging and discharging of the first filter layer and the charging and discharging of the second filter layer. Here, too, the first voltage pulses can in principle be somewhat longer than the second voltage pulses. For example, the first voltage pulses can be applied for 5 seconds, while the second voltage pulses can only be applied for 1 second.

[0014] In this variant not according to the invention, the first and second voltage pulses are preferably rectangular pulses, i.e. pulses with steep edges and constant high voltage levels.

[0015] Alternatively, according to the invention, the first voltage is provided as a first sinusoidal voltage or first trapezoidal voltage and the second voltage as a second sinusoidal voltage or second trapezoidal voltage, wherein the sinusoidal voltages or trapezoidal voltages are provided offset from one another such that the second sinusoidal voltage or second trapezoidal voltage passes through its maximum when the first sinusoidal voltage or first trapezoidal voltage passes through its minimum. In this control variant according to the invention, the charging and discharging process takes place according to a sinusoidal or trapezoidal curve, ie the voltage increases in each case according to the curve shape up to a maximum, from which it drops again to a minimum.The two voltages are now offset from each other in such a way that the second voltage reaches its maximum when the first voltage passes through its minimum, so that consequently the maximum charging of the second filter layer serving for neutralization or discharge occurs when the first filter layer is voltage-free.

[0016] The second sinusoidal voltage or second trapezoidal voltage can have a higher frequency than the first sinusoidal voltage or first trapezoidal voltage. This means that the second voltage is applied superimposed on the first voltage, meaning that the second filter layer is continuously charged and discharged with a correspondingly higher frequency sinusoidal or trapezoidal voltage, while the first filter layer is charged and discharged with a lower frequency sinusoidal or trapezoidal voltage. However, the voltage curves, as described, are such that when the first voltage passes through a minimum, the second voltage reaches its maximum.

[0017] The level of the first and / or second voltage can further be varied depending on at least one environmental parameter and / or at least one operating voltage of a fan that is connected to a ventilation duct operated via the electric air filter. Such an environmental parameter can be, for example, the outside air temperature or the temperature of the air passed through the electric air filter. The higher the outside temperature or air temperature, the lower the high voltage of the first and second filter layers can be. Another environmental parameter can be the outside air humidity or the humidity of the air passed through the electric air filter. The higher the air humidity, the lower the high voltage of the first and second filter layers can be. The current operating voltage of a fan that conveys the air, which is indicative of the air throughput, can also be used as a parameter.

[0018] As described, both filter layers are charged with a high voltage of different polarity. Generally, the first voltage should be higher than the second voltage in terms of magnitude. The first voltage should be in the range between 5 and 10 kV, and the second voltage should be in the range between 1 and 4 kV.

[0019] Preferably the first voltage is negative and the second voltage is positive, but the polarity can be reversed if necessary.

[0020] In addition to the method, the invention further relates to an electrostatic precipitator device, comprising an electric air filter with a first and a separate second filter layer, a first voltage source via which the first filter layer can be charged with a first voltage, a second voltage source via which the second filter layer can be charged with a second voltage having a different polarity than the first voltage, and a control device configured to control the two voltage sources according to the method described above.

[0021] Finally, the invention also relates to a motor vehicle comprising at least one electrostatic precipitator device of the type described above.

[0022] Further advantages and details of the present invention will become apparent from the exemplary embodiments described below and from the drawings. In the drawings: Fig. 1 a schematic diagram of a filter device of a motor vehicle comprising an electric air filter, Fig. 2 a schematic diagram of the electric air filter, Fig. 3 is a schematic diagram showing the high voltage profile at both filter layers according to a first embodiment not according to the invention, Fig. 4 is a schematic diagram of a diagram showing the course of the high voltage at both filter layers according to a second embodiment not according to the invention, Fig. 5 is a schematic diagram showing the high voltage profile at both filter layers according to a third embodiment of the invention, Fig. 6 is a schematic diagram showing the high voltage profile at both filter layers according to a fourth embodiment of the invention, and Fig. 7 is a schematic diagram showing the high voltage profile at both filter layers according to a fifth embodiment of the invention.

[0023] Fig. Figure 1 shows a schematic diagram of a filter device 1 according to the invention, which is part of a ventilation system of a motor vehicle. The filter device 1 comprises an electric air filter device including an electric air filter 2, downstream of which is a standard air filter 3, for example, a combination filter with a pollen filter, an activated carbon filter, and the like. The electric air filter 2 and the air filter 3 are accommodated, for example, in a pipe 4, which is part of the ventilation system. An air stream 5 flows through this pipe 4, which is to be cleaned via the electric air filter 2 and the air filter 3.

[0024] The electric air filter 2 comprises a first filter layer 6 and a second filter layer 7, which are arranged in the pipe 4, which is connected to earth potential 10, via corresponding insulators 8, 9. Both filter layers 6, 7 can be separately supplied with high voltage of different polarity via separate voltage sources. A basic circuit diagram for this is shown in Fig. 2 shown.

[0025] Fig. Figure 2, which shows a purely schematic circuit used to explain the basic functional principle, shows the two filter layers 6, 7, which are formed, for example, as a metal grid or via metal needles. Each filter layer 6, 7 is integrated into its own circuit, via which it can be separately charged with high voltage. The first circuit 11 comprises a first voltage source 12 that provides high voltage. Furthermore, a capacitor 13 is provided in the circuit 11, as an example, across which the high voltage is dropped, as well as a switching means 14, via which the circuit can be opened and closed. Of course, such a switching means is not required, for example, in the case of modulated control and the like, via which the voltage source 12 is directly controlled.The second circuit 15 of the second filter layer 7 comprises a second voltage source 16, which also provides high voltage, but of a different polarity than the first voltage source 12. Here, too, a capacitor 17, across which the high voltage drops, and a switching means 18 are provided merely for illustration purposes.

[0026] Also shown is a control device 19, which, by way of example, controls the two switching devices 14, 18, but can of course also directly control the voltage sources 12, 16 accordingly, for example, when controlling sine or trapezoidal curves. At least one sensor 20 is assigned to the control device 19, via which, for example, the air temperature or humidity can be measured, which environmental information can be incorporated into the control operation, such as the level of the respective applied high voltage or the durations or frequencies of the respective high voltage.

[0027] The control device 19 is now able to control the two circuits 11, 15 differently, so that the first filter layer 6 is alternately charged with high voltage up to a maximum voltage, and the second filter layer 7 is charged with high voltage of opposite polarity up to a maximum voltage. The charging operation is alternating, i.e., at least when the second filter layer passes through its maximum voltage, i.e., the maximum high voltage is applied, the first filter layer passes through a maximum voltage, i.e., no voltage or only a negligible voltage is applied there. This is because, via the second filter layer, a discharge of any statically charged environmental areas around the electric air filter 2 or the air filter 3, as well as downstream areas of the device, occurs through the generation of charged particles that are of opposite polarity to the charges that cause the static charge.The actual cleaning operation takes place via the first filter layer 6. If it is appropriately charged, it is preferably strongly negatively charged, so that it emits electrons that attach to the gas molecules in the air and charge them negatively, or remove electrons from gas molecules, causing the molecules to become positively charged. The charged molecules, in turn, attach to air particles such as dust particles or pollen, which are charged by the first layer, so that they are deposited on a downstream separation electrode, which could be, for example, the second filter layer 2 or the pipe connected to earth potential, or something similar.Since this deposition movement occurs virtually perpendicularly, or at least with a perpendicular motion component relative to the airflow direction, it can happen that charged particles are carried along with the airflow and adhere to locations far from the actual desired deposition position, resulting in the described static charge in these areas. This can now be counteracted by the intermittent operation of the oppositely charged second filter layer 7, since this opposite high-voltage charge creates oppositely charged particles, which can also accumulate at these locations and neutralize the static charge particles.

[0028] Fig. Figure 3 shows a first diagram illustrating a first voltage curve at the two filter layers 6, 7, not according to the invention. The time t is plotted in minutes along the abscissa, and the voltage U in kV is plotted along the ordinate. The curve sections above the abscissa represent the charging voltage of the second filter layer 7, and the curve sections below represent the charging voltage of the first filter layer 6.

[0029] Fig. 3 shows corresponding square-wave voltages, i.e. the first filter layer 6 is constantly negatively charged via a constant first voltage U1 during a first time interval, while the second voltage U2 shown is the constant voltage with which the second filter layer 7 is constantly positively charged during a second time interval. The first time interval is clearly much longer than the second time interval. It is, for example, between 2 and 10 minutes, while the second time interval is between 0.5 and 2 minutes. The voltage U1 is, for example, 6 to 10 kV, while the voltage U2 is, for example, 2 to 4 kV. The control device 19 controls the two circuits 11, 15 or their switching means 14, 18 or, if such are not provided, directly the voltage sources 12, 16 according to this square-wave diagram.The first time interval is for the intended cleaning, the second for the neutralization of any static charge.

[0030] Fig. Figure 4 shows a schematic diagram of a second voltage curve not according to the invention at both filter layers 6, 7, wherein the time is plotted in seconds along the abscissa and the voltage U in kV along the ordinate. Again, a rectangular voltage is provided here, with the voltages U1 and U2, which in turn represent the voltages already Fig. 3. However, the time intervals here are significantly shorter and are in the range of seconds. Thus, a higher-frequency, rapid pulse sequence is present. For example, a time interval in which voltage U1 is applied lasts 5 seconds, and a time interval in which voltage U2 is applied lasts 1 second.

[0031] Fig. 5 shows a schematic diagram of a third voltage curve according to the invention across both filter layers 6, 7, where voltages U1 and U2 are each sinusoidal voltages. In the example shown, voltage U1 has a first frequency and voltage U2 has a second frequency that is twice as high, with the respective voltage minimum being 0 V. The two frequencies are selected such that when voltage U1 passes through a minimum, voltage U2 passes through its maximum, i.e., when voltage U1 passes through a minimum, voltage U2 passes through its maximum. This means that second filter layer 7 is maximally charged when first filter layer 6 is discharged. This sinusoidal curve can be controlled, for example, by directly controlling the respective voltage sources 12, 16 via control device 19. The magnitudes of voltages U1, U2 are again in the kV ranges already specified above.

[0032] Fig. 6 shows a schematic diagram of a fourth voltage curve according to the invention, which is comparable with the Fig. 5. However, here the voltages U1 and U2 are equal in frequency. Therefore, every time voltage U1 passes through a minimum voltage, a maximum voltage U2 occurs.

[0033] Fig. Finally, Figure 7 shows a schematic diagram of a fifth voltage waveform according to the invention, in which the voltages U1 and U2 are each controlled as trapezoidal voltages. Thus, they each have linear edges, over which they run to their respective maximum and minimum. Again, the frequencies are the same, so that for every voltage minimum passed through by voltage U1, voltage U2 passes through its voltage maximum.

[0034] Also in the Fig. 6 and Fig. 7, the amounts of the respective positive and negative high voltages are in the above-specified ranges of 6 - 10 kV for the negative high voltage U1 and of 2 - 4 kV for the positive high voltage U2.

[0035] The two voltage sources 10, 11 can be controlled, in particular for controlling any sinusoidal or trapezoidal voltages, for example via pulse width modulation

Claims

[1] Method for controlling an electric air filter (2) for a vehicle interior of a motor vehicle, wherein a first filter layer (6) is charged with a first voltage (U1) via a first voltage source (12), and a second filter layer (7) is charged with a second voltage (U2) having a different polarity than the first voltage (U1) via a second voltage source (16), wherein the two filter layers (6, 7) are alternately charged and discharged, characterized by , that the first voltage (U1) is given as a first sinusoidal voltage or first trapezoidal voltage and the second voltage (U2) is given as a second sinusoidal voltage or second trapezoidal voltage, wherein the sinusoidal voltages or trapezoidal voltages are given offset from one another in such a way that the second sinusoidal voltage or second trapezoidal voltage passes through its maximum when the first sinusoidal voltage or first trapezoidal voltage passes through its minimum. [2] Method according to claim 1, characterized by that the second sinusoidal voltage or second trapezoidal voltage has a higher frequency than the first sinusoidal voltage or first trapezoidal voltage. [3] Method according to one of the preceding claims, characterized by that the level of the first and the second voltage (U1, U2) is varied depending on at least one environmental parameter and / or at least one operating voltage of a fan which is connected to a ventilation duct operated via the electric air filter (2). [4] Method according to claim 3, wherein an environmental parameter is the outside temperature or temperature of the air passed through the electric air filter or outside air humidity or the humidity of the air passed through the electric air filter (2). [5] Method according to one of the preceding claims, characterized bythat the first voltage (U1) is in the range between 5 - 10 kV and the second voltage (U2) is in the range between 1 - 4 kV. [6] Method according to one of the preceding claims, characterized by that the first voltage (U1) is negative and the second voltage (U2) is positive. [7] Electrostatic precipitator device, comprising an electric air filter (2) with a first and a separate second filter layer (6, 7), a first voltage source (12) via which the first filter layer (6) can be charged with a first voltage (U1), a second voltage source (16) via which the second filter layer (7) can be charged with a second voltage (U2) having a different polarity than the first voltage (U1), and a control device (19) configured to control the two voltage sources according to the method according to one of the preceding claims. [8] Motor vehicle comprising at least one electrostatic precipitator device according to claim 7.

Images