Method for evaluating a capacitance value of a capacitive sensor electrode

Abstract

This invention relates to a method for evaluating the capacitance value of an electrode in a capacitive sensor. The method includes an evaluation process comprising the following steps: - performing a charging process on the sensor electrode; - evaluating parameters related to the capacitance value of the sensor electrode. The first coupling and decoupling cycle is determined by the first coupling duration t. K,1 and the first decoupling duration t E,1 The duration t of the first charging pulse L,1 , t L,1 =t K,1 +t E,1 The duration t of the second coupling cycle following the first coupling and decoupling cycle. K,2 Second decoupling duration t E,2 The duration t of the second charging pulse L,2 , t L,2 =t K,2 +t E,2 The deviation between them is the first pulse duration deviation Δt. L,1 .

Description

Technical Field

[0001] This invention relates to a method for evaluating the capacitance value of electrodes in a capacitive sensor. Background Technology

[0002] As is known in practice, sensor electrodes are used for a variety of purposes.

[0003] An example of using capacitive sensor electrodes is a capacitive proximity switch, which is installed in a vehicle to detect, for example, the presence of a person. The function of such a capacitive proximity switch is based on the fact that the capacitance of the capacitive sensor electrodes of the proximity switch reaches or exceeds a specific value, or undergoes a predetermined absolute or relative change.

[0004] To evaluate capacitance at a specific point in time or over a specific time period, capacitive sensor electrodes are associated with a predetermined potential. The sensor electrode and a reference electrode form a capacitance. In the example of a proximity switch present in a vehicle, the vehicle ground or the ground beneath the vehicle is used as the reference electrode. When a part of a user's body, such as a hand or foot, enters the sensing area of ​​the sensor electrode, the electrostatic properties of the overall system change. Within the scope of equivalent observation, this effect can be understood as a change in the dielectric surrounding the sensor electrode.

[0005] In order to infer information such as the presence of a hand or foot from the capacitance value of the sensor electrodes or from changes in the capacitance value of the sensor electrodes, the capacitance value needs to be evaluated.

[0006] The capacitance value can be evaluated in different ways. For example, it can be set up to repeatedly charge the sensor electrode to a reference potential of the voltage source and then discharge the sensor electrode into a comparison capacitor, with the charge accumulated on the comparison capacitor immediately following the repeated charging and discharging. An example of implementing this principle can be found in DE 196 81 725B4.

[0007] In principle, the capacitance value is evaluated by periodically charging the sensor electrodes, followed by evaluating either the charging process or, in most cases, the discharging process, which is also performed periodically, the capacitance-related parameters.

[0008] The parameter to be evaluated could be, for example, voltage, which is measured on a capacitor that has accumulated charge, as in the example above.

[0009] Other possibilities for the parameters to be evaluated could be a specific number of charge and discharge cycles until a switching threshold on the compensation capacitor is exceeded. An example of such a process is known from DE 10 2013 112 910 A1. In the method described in that document, during the first stage, the capacitive sensor electrode is coupled to the charging voltage via a first switching device to charge the sensor electrode. Simultaneously, the compensation capacitor is coupled between a reference voltage and ground via a second switching device, thereby also charging the compensation capacitor. Charge balancing between the sensor electrode and the compensation capacitor is then performed. The electrode capacitance is determined based on the charge accumulated on the evaluation compensation capacitor.

[0010] Therefore, it is generally established that the methods known in existing technology and practice for evaluating the capacitance value of capacitive sensor electrodes are based on the premise that the sensor electrodes are periodically charged. Depending on the specific implementation, it can be configured that the sensor electrodes are gradually charged over multiple cycles, or that the sensor electrodes are separately (partially or fully) charged and (partially or fully) discharged in each of multiple cycles.

[0011] To ensure reliable evaluation of the sensor electrode capacitance within sufficiently short timeframes, the sensor electrodes are typically charged and, if necessary, discharged at a relatively high frequency. These frequencies are often set in the range of tens to hundreds of kHz.

[0012] The high-frequency charging of sensor electrodes creates a problem (which tends to become more pronounced at higher frequencies): the periodic charging and, if necessary, discharging at high frequencies generates an undesirable alternating electromagnetic field. Depending on the size and shape of the sensor electrodes, the implementation of their manipulation in switching technology, and the chosen frequency, the sensor electrodes act as antennas to a certain extent and emit electromagnetic radiation. This effect can be problematic, especially in the context of regulatory restrictions on products emitting electromagnetic waves. For example, in Germany, numerous restrictions exist based on the German Federal Emissions Protection Act, from which binding limits for electromagnetic emissions are derived. These limits are frequency-dependent and quite stringent. As explained at the beginning of this article, the typically high frequencies used for evaluating sensor electrodes, coupled with stringent regulatory requirements, place high demands on the design and operation of capacitive sensor electrodes. Summary of the Invention

[0013] Against the backdrop of the foregoing ideas, the object of the present invention is to enable the evaluation of the capacitance value of capacitive sensor electrodes and the arrangement of capacitive sensor electrodes, for example, in motor vehicles, with greater flexibility, for example, in terms of shape and installation location.

[0014] This task is solved by a method according to the invention for evaluating the capacitance value of a proximity switch with sensor electrodes in a motor vehicle.

[0015] The purpose of this method is to evaluate the capacitance value of a capacitive sensor electrode. To evaluate the capacitance, the sensor electrode is periodically charged at least once. This periodic charging of the sensor electrode involves the sensor electrode undergoing a certain number of coupling and decoupling cycles. During each coupling and decoupling cycle, the sensor electrode is charged for a coupling duration t. k During this period, the sensor electrode is coupled with the charging circuit. During coupling between the sensor electrode and the charging circuit, the sensor electrode is partially or fully charged. The amount of charge received by the capacitive electrode is related to the capacitance according to the principle relationship C = Q / U, where C: capacitance, Q = charge, and U = voltage. This is followed by the coupling duration t. K The next step is to decouple the sensor electrodes for a duration t. E During this period, it is decoupled from the charging circuit.

[0016] During the coupling duration t K During this period, at least one partial charge is performed on the sensor electrodes. During the decoupling duration t... E No charging of the sensor electrodes is performed during this period. Based on the principle, it can also be set so that during the coupling duration t... K The sensor electrodes are fully charged during this period. During the decoupling duration t... E During this period, it can be configured so that not only are the sensor electrodes not charged, but they are also partially or completely discharged. Regarding the specific implementation of charging the sensor electrodes in terms of circuit technology, various implementation schemes can be provided to those skilled in the art. For example, this can be achieved by coupling the sensor electrodes to the evaluation circuit and / or by recharging the charge present on the sensor electrodes to the compensation capacitor, thus achieving a decoupling duration t. E The decision to interrupt charging or to discharge the sensor electrodes depends on the selection of the evaluation method and the specific implementation by those skilled in the art.

[0017] The term "circuit," as understood by those skilled in the art, is generally understood to refer to structural elements of electronic devices that are electrically connected to each other. Therefore, within the scope of this application, the term "circuit" is generally used synonymously with the term "circuit," where each type of circuit can be used to implement the invention. In specific embodiments of the invention, the term "circuit" can also refer to an integrated circuit; thus, the following embodiments of the invention are also possible, in which one or more circuits are configured as an integrated circuit or are simply integrated circuits.

[0018] Regardless of the specific execution of the evaluation of the capacitance of the sensor electrodes, the fundamental premise for executing the method according to the invention is that the sensor electrodes are periodically charged or periodically continuously charged.

[0019] The method according to the invention includes the step of evaluating parameters related to the capacitance value of the sensor electrodes. This evaluation of parameters related to the capacitance value of the sensor electrodes can be performed in each coupling and decoupling cycle, in more than one but not all coupling and decoupling cycles, or only after all coupling and decoupling cycles have ended.

[0020] Parameters considered for evaluating capacitance values ​​may include, for example, voltage variation curves at the terminals of the sensor electrodes, voltage measured on a capacitor accumulating charge, or charging and / or discharging for a specific number of cycles until the voltage measured at the sensor electrodes exceeds the switching threshold.

[0021] The method steps of coupling the sensor electrode to the charging circuit and decoupling the sensor electrode from the charging circuit, as well as the comparative parameters for obtaining the capacitance value or reflecting the capacitance value, are known to those skilled in the art, as are known from the literature mentioned at the beginning of this document.

[0022] The method according to the invention differs from well-known procedures in that multiple coupling and decoupling cycles are performed during the evaluation process, and the duration of these cycles varies. In other words, the pulse frequency of the coupling and decoupling durations during the evaluation process is variable.

[0023] In other words, at least one first charging pulse duration t is set. L,1 Second charging pulse time t L,2 The duration of the first charging pulse is generally determined by the first coupling duration t. K,1 and the first decoupling duration t E,1 Composition. Duration t of the second charging pulse. L,2 Overall, it is determined by the second coupling duration t K,2 Second decoupling duration t E,2 composition.

[0024] In the nomenclature used here, the durations of the first and second charging pulses are the charging pulse durations of the first and second coupling and decoupling cycles that are directly consecutive. However, it is not mandatory to refer to the first two coupling and decoupling cycles of the evaluation process, but can refer to two directly consecutive coupling and decoupling cycles at any point in a series of coupling and decoupling cycles of the evaluation process.

[0025] According to the present invention, the difference between the duration of the first charging pulse and the duration of the second charging pulse lies in their lengths. The duration of the first charging pulse deviates from the duration of the second charging pulse by a deviation amount Δt. L,1 Mathematically, this is expressed as the pulse duration deviation Δt. L,1 =t L,2 -t L,1 .

[0026] Because the duration of the charging pulse used during the evaluation process changes according to the invention, the emission characterization of the sensor electrode is advantageously affected during the evaluation of the sensor electrode's capacitance. The change in charging pulse duration reduces the maximum value of the frequency-dependent emission power density, which is beneficial for broadening the signal spectrum bandwidth. The frequency-dependent emission peaks are thus truncated and their height is reduced. In other words, a wider distribution of emission energy density at the emission frequency is achieved. Furthermore, the emission of higher harmonics is avoided or at least its influence is significantly reduced.

[0027] This invention therefore utilizes the understanding that, in capacitive sensor electrodes using known and commonly used evaluation methods, charging the sensor electrodes at excessively high charging frequencies can lead to several problematic effects. These effects can be reduced or even avoided by varying the charging frequency. The process according to the invention allows for greater flexibility in the design of the sensor electrodes and the execution of capacitance evaluation within the framework required by regulations, such as those described at the beginning of this document. Because the frequency-related energy density is more widely distributed across the frequency scale and the amplitude maximum is smaller, higher frequencies can be used for evaluation overall. This also has the advantage of increased evaluation speed. A significant advantage of the technical solution according to the invention is that the duration of the charging pulse can be varied by, for example, manipulating the charging circuit or a corresponding evaluation circuit in general. The implementation of the method according to the invention can therefore be carried out by correspondingly matching control electronics and, optionally, by purely software matching. It can also be built on existing hardware if desired, resulting in cost advantages.

[0028] Preferably, the evaluation process is performed in multiple coupling and decoupling cycles, with the number of coupling and decoupling cycles being between 100 and 500, and particularly preferably between 150 and 250.

[0029] In particular, according to an advantageous improvement, the durations of the first and second charging pulses are set between 1.0 μs and 10.0 μs, preferably between 2.5 μs and 4.0 μs. Reliable results are typically achieved within a very short time at the resulting coupling and decoupling frequencies between 250 kHz and 400 kHz.

[0030] The duration of all charging pulses in the evaluation process, i.e. all coupling and decoupling cycles, is preferably between 1.0 μs and 10.0 μs, and more preferably between 2.5 μs and 4.0 μs.

[0031] According to the first alternative scheme, the pulse duration deviation Δt can be set. L,1 This is adjusted by changing the decoupling duration; therefore, the duration t of the first charging pulse... L,1 Second charging pulse duration t L,2 The only difference is the decoupling duration, where the coupling duration is maintained and is the same for both the first and second coupling and decoupling cycles.

[0032] In another alternative process, the duration of the charging pulse between the first coupling and decoupling cycle and the second coupling and decoupling cycle is adjusted by changing the coupling duration while maintaining the decoupling duration.

[0033] Another alternative scheme is a hybrid of the two alternative schemes mentioned above, namely, the pulse duration deviation Δt. L,1 This is caused not only by changing the duration of coupling but also by changing the duration of decoupling.

[0034] To change the duration of the charging pulse, it can be set such that, within an evaluation process having N coupling and decoupling cycles (which are, for example, consecutively labeled with integer footnotes i from 0 to N-1), the duration t of two consecutive coupling and decoupling cycles with footnote numbers i and i+1 is... L,i+1 and t L,i Pulse duration deviation Δt L,i For at least 50% of the coupling and decoupling cycles, there is a relative deviation |Δt| from the value of the charging pulse duration. L,i | / t L,i≥0.1. In other words, it should be set such that, in at least 50% of the coupling and decoupling cycles, there is a pulse duration deviation relative to the immediately preceding coupling and decoupling cycle, and this pulse duration deviation changes the duration of the corresponding immediately preceding charging pulse by at least 10%. In a preferred improvement, this change exists not only in 50% of the coupling and decoupling cycles of the evaluation process, but also in at least 80%, and in particularly preferred processes, even in 100% of the coupling and decoupling cycles.

[0035] In an improved version of the method, a minimum and a maximum charging pulse duration are predetermined, along with a certain number of predetermined charging pulse duration values. Two consecutive coupling and decoupling cycles are controlled using two different predetermined charging pulse duration values. Therefore, the charging pulse duration is not randomly manipulated or calculated based on the coupling and / or decoupling durations; instead, for example, a list exists on the microcontroller controlling the method, containing at least two preferred pairs of coupling and decoupling duration values, upon which changes in the charging pulse duration are controlled.

[0036] Specifically, the predetermined charging pulse duration values ​​can be equidistantly distributed between the minimum and maximum charging pulse durations. For example, a minimum and maximum charging pulse duration can be predetermined, both between 1.0 μs and 10 μs, with a certain number of equidistant charging pulse duration values ​​between the minimum and maximum durations. Preferably, 1.5 μs is set as the minimum charging pulse duration and 5.0 μs as the maximum charging pulse duration; particularly preferably, 2.0 μs is set as the minimum charging pulse duration and 4.0 μs as the maximum charging pulse duration. These charging pulse durations can be predetermined directly or through a combination of corresponding coupling and decoupling durations.

[0037] The duration of the charging pulses can be used to control the charging circuit in a predetermined or random order.

[0038] Alternatively, the duration of the charging pulses can be changed via predetermined maximum and minimum charging frequencies. A number of predetermined charging pulse frequencies can be set, wherein two consecutive coupling and decoupling cycles are controlled by two different predetermined charging pulse frequencies. In particular, the charging pulse frequencies can be equidistantly distributed between the maximum and minimum charging frequencies. The charging pulse frequencies can be selected in a predetermined order or a random order. In principle, this is the same process as directly selecting a predetermined charging pulse duration; depending on the implementation scheme, charging pulse frequencies that are reciprocals of the charging pulse duration can be observed more flexibly. Similar to the preferred charging pulse duration set above, the minimum and maximum charging frequencies can be set between 1000 kHz and 100 kHz, preferably between 667 kHz and 200 kHz, and particularly preferably between 400 kHz and 250 kHz.

[0039] An exemplary method sequence for implementing the process according to the present invention includes performing the following steps:

[0040] - During the coupling and decoupling cycle, during the coupling duration t K During this period, the sensor electrodes are fully charged using a predetermined charging voltage from the charging circuit.

[0041] - During the decoupling duration t E During this process, after the sensor electrodes are decoupled from the charging circuit, they are coupled to the storage circuit. The storage circuit has a storage capacitance C. L Due to the coupling between the sensor electrodes and the storage circuit, the charge carriers stored in the sensor electrodes are transferred to the storage capacitor C. L And then the recharging is carried out on the ground.

[0042] Within multiple coupling and decoupling cycles, the sensor electrodes are fully recharged during the coupling duration of each coupling cycle. During the subsequent decoupling duration, the charge from the recharged sensor electrodes is used to power the storage capacitor C. L Continuously, but not necessarily completely, load cells are applied.

[0043] The evaluation of parameters related to the capacitance value of the sensor electrode includes detecting the voltage accumulated on the storage capacitor after a certain number of coupling and decoupling cycles, preferably after a predetermined number of coupling and decoupling cycles, and taking into account the voltage of the sensor electrode or the value related to the capacitance of the sensor electrode.

[0044] The evaluation here is based in particular on the correlation of carrier recharging between two capacitors or capacitances, which is well known to those skilled in the art. Based on this correlation, the capacitance of the sensor electrode, or parameters related to that capacitance, can be inferred from the voltage on the storage capacitor after a certain number of recharging processes between a fully charged sensor electrode and an uncharged or partially charged storage capacitor.

[0045] Those skilled in the art are dedicated to precise implementation. It is reasonable that C... L The capacitance is greater than that of the sensor electrodes. C L The capacitance can be, for example, at least several times the capacitance of the sensor electrodes, and preferably has a factor corresponding to or exceeding a predetermined number of coupling and decoupling cycles. L Ideally, the battery should be fully discharged before the first coupling and decoupling cycle. A value is also chosen for the coupling and decoupling durations, allowing for the desired end of recharging. This is given in the order of magnitude of the charging pulse durations mentioned in this application.

[0046] As explained at the beginning of this document, multiple charging of the sensor electrodes is important for this invention. The deviation of the duration of the second charging pulse from the duration of the first charging pulse, according to the invention, avoids or, in effect, suppresses transmission effects that could undesirably cause the sensor electrodes to function as antennas.

[0047] Another exemplary method sequence for implementing the process according to the present invention includes:

[0048] - During the coupling and decoupling cycles, the sensor electrodes are coupled to the storage circuit. The storage circuit has a storage capacitance C. L Storage capacitor C L It is charged once at a predetermined charging voltage before the first coupling and decoupling cycle. The coupling between the sensor electrodes and the storage circuit causes a charge balance between the storage capacitor and the sensor electrodes.

[0049] - During the decoupling duration t E During this period, for example, the sensor electrodes are fully discharged through a temporary connection to the ground potential.

[0050] - In multiple coupling and decoupling cycles, the sensor electrodes are charged with the charge of the storage capacitor in each coupling cycle. This causes the storage capacitor to be charged in the subsequent coupling and decoupling cycles, based on the decoupling duration t in each cycle. E The discharge of the sensor electrodes is repeated during this period in a continuous, but not necessarily complete, manner.

[0051] The parameters related to the capacitance value of the sensor electrode include detecting the voltage accumulated on the storage capacitor after a certain number of coupling and decoupling cycles in a plurality of coupling and decoupling cycles, preferably after a predetermined number of coupling and decoupling cycles, and using it to determine the capacitance of the sensor electrode or to determine a value related to the capacitance of the sensor electrode.

[0052] Those skilled in the art are dedicated to precise implementation. It is reasonable that C... L The capacitance is greater than that of the sensor electrodes. C L The capacitance can be, for example, at least several times the capacitance of the sensor electrodes, and preferably has a factor corresponding to or exceeding a predetermined number of coupling and decoupling cycles. A value is also selected for the coupling and decoupling duration, which is required for the recharging process. This is given in the order of magnitude of the charging pulse duration mentioned in this application. Due to the repeated discharge toward the sensor electrodes, the voltage at capacitance C... L The rate of decrease is also related to the capacitance of the sensor electrodes, in a relationship known to those skilled in the art. This correlation is used, by C L The measured voltage can be used to infer the capacitance of the sensor electrodes or a value related to that capacitance, such as the relative change in the capacitance of the sensor electrodes.

[0053] In this feasible implementation, the sensor electrodes are repeatedly charged, so that the potential adverse effects of the sensor electrodes are mitigated by changing the duration of the charging pulse according to the invention.

[0054] Particularly preferred is that the described method is applied to evaluate the capacitance or capacitance change of a proximity switch with sensor electrodes in a motor vehicle. Attached Figure Description

[0055] The accompanying drawings illustrate the invention described above and its improvements. It should be understood that the features mentioned above and those to be described below can be used not only in combinations described separately, but also in other combinations or individually.

[0056] in:

[0057] Figure 1a : A schematic diagram illustrating an exemplary charging process of the sensor electrodes, known in practice;

[0058] Figure 1b : Shown in Figure 1a A schematic diagram showing the emission characteristics of the sensor electrodes during the charging process;

[0059] Figure 2a : A schematic diagram showing the charging process of a sensor electrode used to evaluate the capacitance value of a sensor electrode according to the present invention;

[0060] Figure 2b : Shown in Figure 2a The diagram shows the emission characteristics of the sensor electrodes during the charging process.

[0061] Figure 3 : A schematic diagram illustrating an exemplary design of a capacitive proximity sensor device in which a method flow according to the invention is performed. Detailed Implementation

[0062] Figure 1a The coupling and decoupling durations within a segment of the charging process captured for evaluating the capacitance of the sensor electrode are shown. The correlation between the voltage U applied to the sensor electrode and time t is also shown. As indicated, the charging voltage U... L During the coupling duration t k,i The medium is applied to the sensor electrodes, and then during the decoupling duration t E,i The charging potential is then separated from the sensor electrodes. This process repeats multiple coupling and decoupling cycles, during which... Figure 1a The diagram shows 1 to 4 coupling and decoupling cycles, denoted by t. K,i and t E,i This indicates that i = 0…3. In Figure 1a The diagram applies to coupling and decoupling cycles i = 0…N-1 out of a total of N cycles in the evaluation process, where t K,1 =t K,2 =t K,3 =t K,4 =t K,i Similarly, t E,1 =t E,2 =t E,3 =t E,4 =t E,i This applies to all i = 0…N-1. (Based on...) Figure 1a The manipulation of the coupling between the sensor electrodes and the charging circuit resulted in the sensor electrodes in... Figure 1b The emission characteristics are schematically shown in the diagram. Figure 1b The transmit power P related to frequency f is shown. A Among them, at the charging pulse frequency f L The maximum value of the emission characteristics is reached at this time, and the frequency of this charging pulse is determined by the duration t of the charging pulse. i =t L,1 =t K,1 +t E,1 =1 / f L The conclusion is as follows.

[0063] Depend on Figure 2aThe improved method according to the invention can be seen in exemplary variations. In the method from Figure 2a In the implementation plan to be known, the decoupling duration t E,i (i = 0…N-1) remains unchanged; however, the duration of the charging pulse is changed by altering the coupling duration. Specifically, the coupling duration t… K,0 ≠t K,1 ≠t K,2 ≠t K,3 In the figure shown, the decoupling duration of 2.5 μs remains constant for all coupling and decoupling cycles, and the coupling duration changes from t... K,0 =0.5μs, and increased to t by gradually increasing in 0.5μs intervals. K,3 = 2.0 μs. Therefore, in the design scheme shown, in two consecutive coupling and decoupling cycles, after reaching a coupling duration of 2.0 μs and before setting the coupling duration to 0.5 μs again in the immediately following coupling and decoupling cycle, the pulse duration deviation is Δt. L,0 =Δt L,1 =Δt L,2 =0.5μs, which in the example shown results in a pulse duration deviation of |Δt|. L,3 |=1.5μs. The change in charging pulse duration in the example shown is performed in a predetermined order, wherein the predetermined order sets the coupling duration to increase sequentially from the minimum to the maximum value as shown and illustrated, and thus sets the charging pulse duration to increase sequentially and continuously from the minimum charging pulse duration to the maximum charging pulse duration. However, in principle, based on the above description, other orders of coupling duration are also possible within the framework of the present invention.

[0064] Figure 2b For example, it was learned that in Figure 2a The diagram shows a schematic representation of the emission characteristics of the sensor electrodes during the charging process. In particular, the maximum emission power P... A,max Compared to Figure 1b The maximum value of the frequency-dependent transmit power shown in the figure is greatly reduced, while the function P A,max exist Figure 2b The half-value width in the representation shown is relative to Figure 1b The interrelationships on the functions shown are significantly broadened.

[0065] Figure 3 A schematic diagram of an exemplary design of a capacitive proximity sensor device is shown, in which the method according to the invention is performed.

[0066] The proximity sensor device 1 has sensor electrodes, which are connected to a capacitor C. S Symbolically represented. Sensor electrodes in Figure 3 a) is coupled to the charging circuit to supply voltage V DD On the other hand, C S With storage capacitor C L Connecting storage loops in series is also feasible.

[0067] Switches S1 and S2 can be controlled via a microcontroller μC. This is for performing a recharging process, for example... Figure 1a In the first step shown, the sensor electrode C is... S Coupled with the charging circuit to be used at the charging voltage V DD The sensor electrodes are then charged. Afterwards, S1 is opened and S2 is closed (in this order) so that C is electrically and effectively charged. S and C L The coupling is formed into a series connection of capacitors. The result is that in C... S and C L The carrier balance between them is achieved. This process is repeated until the recharge process n is reached. U,i The predetermined number of capacitors are charged continuously until the desired operating point is reached. This concludes the recharge cycle.

[0068] Of course, in addition to the embodiments shown, many other embodiments are also possible, in which the method according to the invention can be performed in its own way.

Claims

1. A method for evaluating the capacitance value of a proximity switch with sensor electrodes in a motor vehicle, wherein, The evaluation process includes the following steps: - Perform a charging process for the sensor electrodes, wherein the sensor electrodes are coupled to the charging circuit for a coupling duration t during multiple coupling and decoupling cycles. K And it was decoupled from the charging circuit for a decoupling duration t. E , In the coupling and decoupling cycle, during the coupling duration t K During this period, at least a portion of the sensor electrodes are charged, and wherein, during the decoupling duration t... E The sensor electrodes are not charged during this period. - Evaluate parameters related to the capacitance value of the sensor electrodes, which are stored in the storage capacitance C. L The voltage on the sensor electrode is either charged or discharged for several cycles until the voltage measured on the sensor electrode exceeds the switching threshold, wherein the storage capacitor is the storage capacitor of the storage circuit, and the sensor electrode is coupled to the storage circuit during the coupling and decoupling cycles. The characteristic is that the first coupling and decoupling cycle is determined by the first coupling duration t. K,1 and the first decoupling duration t E,1 The duration t of the first charging pulse L,1 , t L,1 =t K,1 +t E,1 The duration t of the second coupling cycle following the first coupling and decoupling cycle. K,2 Second decoupling duration t E,2 The duration t of the second charging pulse L,2 , t L,2 =t K,2 +t E,2 The deviation between them is the first pulse duration deviation Δt. L,1 .

2. The method according to claim 1, characterized in that, During the evaluation process, the sensor electrodes undergo between 100 and 500 coupling and decoupling cycles.

3. The method according to claim 1 or 2, characterized in that, The duration of the first charging pulse and the duration of the second charging pulse are between 1.0 μs and 10.0 μs.

4. The method according to claim 1 or 2, characterized in that, During the duration of coupling t K,2 =t K,1 In this case, by changing the decoupling duration to the value t E,2 -t E,1 =Δt L,1 To adjust the pulse duration deviation Δt L,1 .

5. The method according to claim 1 or 2, characterized in that, During the decoupling duration t E,2 =t E,1 In this case, by changing the value t of the coupling duration K,2 -t K,1 =Δt L,1 To adjust the pulse duration deviation Δt L,1 .

6. The method according to claim 1 or 2, characterized in that, The pulse duration deviation Δt is adjusted by changing the coupling duration and by changing the decoupling duration. L,1 Wherein, the pulse duration deviation Δt L,1 Having the value Δt L,1 =t K,2 -t K,1 +t E,2 -t E,1 .

7. The method according to claim 1 or 2, characterized in that, During the evaluation process with N coupling and decoupling cycles, the charging pulse duration t L,i With Δt L,i =t L,i+1 -t L,i For the scale of variation, for at least 50% of i = 0…N-1, |Δt L,i | / t L,i >0.

1.

8. The method according to claim 1 or 2, characterized in that, A minimum and a maximum charging pulse duration are predetermined, wherein a certain number of predetermined charging pulse duration values ​​are set, and two consecutive coupling and decoupling cycles are controlled by two different predetermined charging pulse duration values, or... A maximum and minimum charging frequency are predetermined, wherein a certain number of predetermined charging pulse frequencies are set, and two consecutive coupling and decoupling cycles are controlled by two different predetermined charging pulse frequencies.

9. The method according to claim 8, characterized in that, The predetermined charging pulse duration values ​​are evenly distributed between the minimum and maximum charging pulse durations, or The charging pulse frequencies are equidistantly distributed between the maximum charging frequency and the minimum charging frequency.

10. The method according to claim 8, characterized in that, - Control the duration or frequency of the charging pulses in a predetermined sequence, or - Manipulate the duration or frequency of the charging pulses in a random order.

11. The method according to claim 8, characterized in that, The minimum charging pulse duration and the maximum charging pulse duration are between 1.0 μs and 10.0 μs, or The minimum charging frequency and the maximum charging frequency are between 1000 kHz and 100 kHz.

12. The method according to claim 1 or 2, characterized in that, During the coupling and decoupling cycle, during the coupling duration t K During this period, the sensor electrodes are fully charged with charge carriers using a predetermined charging voltage from the charging circuit. Wherein, during the decoupling duration t E During this period, after the sensor electrodes are decoupled from the charging circuit, the sensor electrodes are connected to a circuit with a storage capacitor C. L The storage circuit is coupled to direct the charge carriers stored in the sensor electrodes toward the storage capacitor C. L And then go to the ground for recharging. In this process, during multiple coupling and decoupling cycles, the sensor electrodes are fully recharged during the coupling duration within each coupling cycle, while the capacitor C is charged during the decoupling duration. L Continuous, but not necessarily complete, charging of charge carriers. The evaluation of parameters related to the capacitance value of the sensor electrode includes: detecting the voltage accumulated on the storage capacitor after a certain number of coupling and decoupling cycles in a plurality of coupling and decoupling cycles, and using it to determine the capacitance of the sensor electrode or to determine a value related to the capacitance of the sensor electrode.

13. The method according to claim 1 or 2, characterized in that, During the coupling and decoupling cycle, during the coupling duration t K During this period, the sensor electrode is coupled to the storage circuit to achieve charge balance between the storage capacitor and the sensor electrode. The storage circuit has a storage capacitor C that is charged once at a predetermined charging voltage before the first coupling and decoupling cycle. L , Wherein, during the decoupling duration t E During this period, the sensor electrodes are completely discharged. In this process, during multiple coupling and decoupling cycles, the sensor electrodes are charged with the charge of the storage capacitor in each coupling cycle, thereby continuously, but not necessarily completely, discharging the storage capacitor. The evaluation of parameters related to the capacitance value of the sensor electrode includes: detecting the voltage accumulated on the storage capacitor after a certain number of coupling and decoupling cycles in a plurality of coupling and decoupling cycles, and using it to determine the capacitance of the sensor electrode or to determine a value related to the capacitance of the sensor electrode.

14. The method according to claim 2, characterized in that, During the evaluation process, the sensor electrodes undergo coupling and decoupling cycles of between 150 and 250.

15. The method according to claim 3, characterized in that, The duration of the first charging pulse and the duration of the second charging pulse last between 2.5 μs and 4.0 μs.

16. The method according to claim 7, characterized in that, During the evaluation process with N coupling and decoupling cycles, the charging pulse duration t L,i With Δt L,i =t L,i+1 -t L,i For the scale of variation, for at least 80% of i = 0…N-1, |Δt L,i | / t L,i >0.

1.

17. The method according to claim 7, characterized in that, During the evaluation process with N coupling and decoupling cycles, the charging pulse duration t L,i With Δt L,i =t L,i+1 -t L,i To vary by scale, for 100% of i = 0…N-1, |Δt L,i | / t L,i >0.

1.

18. The method according to claim 11, characterized in that, The minimum charging pulse duration and the maximum charging pulse duration are between 1.5 μs and 5.0 μs.

19. The method according to claim 11, characterized in that, The minimum charging pulse duration and the maximum charging pulse duration are between 2.5 μs and 4.0 μs.

20. The method according to claim 11, characterized in that, The minimum charging frequency and the maximum charging frequency are between 667 kHz and 200 kHz.

21. The method according to claim 11, characterized in that, The minimum charging frequency and the maximum charging frequency are between 400 kHz and 250 kHz.

22. The method according to claim 12, characterized in that, The evaluation of parameters related to the capacitance value of the sensor electrode includes: after a predetermined number of coupling and decoupling cycles, detecting the voltage accumulated on the storage capacitor and using it to determine the capacitance of the sensor electrode or a value related to the capacitance of the sensor electrode.

23. The method according to claim 13, characterized in that, The evaluation of parameters related to the capacitance value of the sensor electrode includes: after a predetermined number of coupling and decoupling cycles, detecting the voltage accumulated on the storage capacitor and using it to determine the capacitance of the sensor electrode or a value related to the capacitance of the sensor electrode.

24. The method according to claim 13, characterized in that, During the decoupling duration t E During this period, the sensor electrodes are fully discharged through a temporary connection to the ground potential.

Images