Switch control element

Abstract

A switching control element, in particular for a motor vehicle (1), in the form of a control panel with an actuating surface (6) for manual operation by means of an element (7), wherein the element (7) is in particular a human hand, with a capacitively operating sensor (9) cooperating with the actuating surface (6) such that the sensor (9) generates a signal (10) when the element (7) approaches the actuating surface (6) and / or when the actuating surface (6) is touched by means of the element (7) and / or when pressure is applied to the actuating surface (6) by means of the element (7), and wherein the signal (10) serves to switch and / or trigger a function in the form of a switching and / or control signal, wherein the capacitively operating sensor (9) comprises an electrical resonant circuit (11), a signal generator (12) for exciting the resonant circuit with an excitation frequency (fmess1),The device comprises a measuring unit (13) for measuring a measured value of the resonant circuit (11) at the excitation frequency (fmess1), in particular the electrical voltage applied to the resonant circuit (11) and / or the electrical current flowing in the resonant circuit (11), and an evaluation unit (14) for generating the signal (10) as a function of the change in the measured value when the element (7) acts on the actuating surface (6), characterized in that the excitation frequency (fmess1) is lower than the resonance frequency (fres) of the resonant circuit (11), in particular that the excitation frequency (fmess1) is selected in a range of approximately 6% to 4% below the resonance frequency (fres), preferably at approximately 5% below the resonance frequency (fres).

Description

[0001] The invention is based on a switching control element according to the preamble of claim 1.

[0002] Such control elements are used in motor vehicles to allow a user to operate a wide variety of functions. For example, the control element can be installed in the form of a control panel in the steering wheel, dashboard, center console, armrest, or similar location within the vehicle. In particular, such a control element is also used as a door handle sensor to detect when a user operates the car door to lock and / or unlock it.

[0003] Such a control element, in the form of a control panel, has an actuation surface for manual operation by the user. This element can be, in particular, a human hand, which is used to actuate the control element. The actuation surface interacts with a capacitive sensor such that the sensor generates a signal when the user approaches the actuation surface, makes contact with it, or applies pressure to it. This signal is used to switch and / or trigger an associated function in the vehicle, acting as a switching and / or control signal.

[0004] The capacitive sensor comprises an electrical resonant circuit, a signal generator for exciting the circuit at a specific frequency, and a measuring unit for measuring the circuit's output at that frequency. Specifically, the measuring unit measures the voltage applied to the resonant circuit and / or the current flowing within it. Furthermore, the sensor includes an evaluation unit that generates a signal based on the change in the measured value when the sensor interacts with the actuating surface. It has been observed that contamination and / or water exposure of the actuating surface can lead to faulty signal generation and, consequently, to the incorrect activation of the associated functions.

[0005] The invention is based on the objective of further developing the switching control element in such a way as to increase its functional reliability. In particular, undesirable response behavior of the capacitive sensor should be largely avoided, even in the presence of contamination and / or water exposure.

[0006] This problem is solved in a generic switching control element by the characterizing features of claim 1.

[0007] In the switching element according to the invention, the excitation frequency is selected such that it is lower than the resonant frequency of the resonant circuit. In particular, the resonant circuit is operated with an excitation frequency that lies in the range of approximately 6% to 4% below the resonant frequency. Preferably, the excitation frequency is selected to be approximately 5% below the resonant frequency. It has been advantageously found that a switching element operated in this manner is largely insensitive to water and / or dirt. Further embodiments of the invention are the subject of the dependent claims.

[0008] In a further embodiment, characterized by particular simplicity and / or functional reliability, the evaluation unit can be configured to generate the signal only when the difference between the measured value at the excitation frequency and the baseline measured value for the unaffected resonant circuit at the excitation frequency exceeds a predefined baseline threshold. The baseline measured value is derived from the undamped resonant circuit, i.e., one in which there is no effect of the element on the actuating surface and / or disturbances such as the effects of water, dirt, or the like. Based on the baseline threshold, the switching element detects the effect of the element when the measured value changes by at least the baseline threshold. This prevents false activations of the switching element.In this process, a so-called baseline can be established in the evaluation unit from the signal extracted from the resonant circuit, i.e., from the measured value. Thus, there is no fixed detection threshold, but rather a dynamic detection threshold for operating the switching element, whereby the dynamic detection threshold is formed from the baseline plus the basic threshold value, similar to a threshold.

[0009] To further increase the operational reliability of the switching element, the signal generator can be configured to excite the resonant circuit at an additional excitation frequency. This additional excitation frequency can be approximately equal to the resonant circuit's resonance frequency. Furthermore, the measuring unit takes an additional measurement at this additional excitation frequency. The evaluation unit only generates the signal if the difference between this additional measurement and the limit value for the unaffected resonant circuit at this additional excitation frequency falls below a predefined threshold. In other words, the signal change of the resonant circuit during operation at the measurement frequency is compared to the signal change of the resonant circuit during operation at the resonance frequency.This allows for the detection of water and / or dirt contamination even when the trigger threshold is exceeded during operation at the measuring frequency, as the signal attenuation during operation at the resonant frequency is then significantly greater. Advantageously, this allows for the detection of a supposed activation of the switching element caused by heavy contamination with water and / or dirt, thus preventing a malfunction of the switching element.

[0010] Furthermore, to improve operational reliability, the signal generator can be configured to excite the resonant circuit with at least one additional excitation frequency close to the excitation frequency. In particular, this additional excitation frequency can be approximately ±0.1% to ±0.6% away from the excitation frequency, preferably approximately ±0.3% to ±0.6% away from the excitation frequency. The measuring unit then measures an additional measurement value at this additional excitation frequency. The evaluation unit generates the signal only if the difference between the additional measurement value and the measurement value is small. In particular, a maximum value can be provided so that the signal is only generated if the difference is less than the specified maximum value. In other words, several closely spaced measurement frequencies are considered.For example, measurements are taken at one or two additional frequencies very close to the measurement frequency. If the changes in the measured values ​​at these additional frequencies are essentially comparable to the change in the measured value at the measurement frequency, for example, a slight increase, then this indicates operation of the switching element. If, however, these changes fluctuate significantly, especially both positively and negatively, this suggests the influence of water and / or dirt. In this case, the signal is not generated.

[0011] In a simple design, the resonant circuit can comprise an inductor and at least one capacitor. In a more cost-effective and compact embodiment, the capacitor and / or the inductor can be implemented as printed circuit components. Advantageously, the capacitor and / or the inductor are arranged on a printed circuit board. Furthermore, the actuating surface, in the form of a sensor electrode, can be part of the capacitor. Finally, a housing with a housing wall can be provided to protect the switching element. The housing wall can form the actuating surface, particularly in the form of a coupling capacitor to the environment.

[0012] In a further embodiment of the switching element, a control and / or monitoring unit can be provided. Advantageously, the control and / or monitoring unit can set the excitation frequency at the signal generator and thus serve to operate the switching element. In a compact design, the evaluation unit can be formed by the control and / or monitoring unit. In a cost-effective manner, the control and / or monitoring unit can be a microcontroller, a microprocessor, or the like.

[0013] In a preferred application for the switching control element, a drive for moving a locking element, in particular for opening it, can be provided. The locking element can be a door, such as a car door, a tailgate, a hood, or the like, of a motor vehicle. The signal generated by the switching control element when operated by the user can then control the drive for the locking element.

[0014] Furthermore, a method related to the invention for operating a capacitive sensor with an electrical resonant circuit, which is particularly intended for a switching control element designed in the form of a control panel, is explained. In such a switching control element, an actuating surface of the switching control element is acted upon by means of an element, which is in particular a human hand. The actuating effect is such that a signal can be generated when the element approaches the actuating surface and / or when the actuating surface is touched by the element and / or when pressure is exerted on the actuating surface by means of the element.For this purpose, the resonant circuit is excited at a specific frequency, and a measurement of the resonant circuit at this frequency is taken, specifically the electrical voltage applied to the circuit and / or the electrical current flowing within it. The change in this measurement, detected when the element acts on the actuating surface, is then used to generate the signal. The excitation frequency is chosen to be lower than the resonant frequency of the circuit. In particular, the excitation frequency is selected to be in a range of approximately 6% to 4% below the resonant frequency, and preferably around 5% below the resonant frequency.

[0015] In a further embodiment of the operating procedure for the capacitive sensor, the signal is only generated if the difference between the measured value at the excitation frequency and the baseline measured value for the unaffected resonant circuit at the excitation frequency exceeds a predefined baseline threshold. An unaffected resonant circuit is defined as one in which the element has no effect on the actuating surface and in which no water and / or dirt is present on the actuating surface.

[0016] Furthermore, to improve operational and / or functional reliability, the resonant circuit can be excited at an additional excitation frequency. In particular, the resonant frequency of the circuit can be selected as the additional excitation frequency. An additional measurement is then taken at this additional excitation frequency. The signal is only generated if the difference between this additional measurement and the limit value for the unaffected resonant circuit at the additional excitation frequency falls below a predefined threshold value.

[0017] The following points should be noted regarding the design.

[0018] The aim is to improve a capacitive sensor with regard to undesirable response to contamination and / or water exposure. In particular, an improved method for measuring and evaluating the signals generated by an LC (inductance / capacitance) resonant circuit is to be specified.

[0019] Capacitive proximity and / or touch sensors are used in various applications on vehicle exteriors. For example, they can be installed or integrated into the exterior door handle, sensors in the underbody area of ​​the tailgate, or similar locations. These sensors detect a person approaching or touching the outer housing by measuring the electrical capacitance. The primary operating principle for capacitance measurement is charge transfer, in which electrical charge is transferred from the electrical evaluation unit to the sensor electrode. A change in the capacitance ratio, internal and / or external, then serves as the detection criterion. However, due to the application and / or design, the capacitance change to be detected is very small, ranging from approximately 100 fF (femtofarads) to 1 pF (picofarads).The critical challenge here has been to reliably and / or reproducibly detect these very small changes under all environmental conditions.

[0020] According to the invention, the capacitive sensor is formed by a resonant circuit comprising an arrangement of at least one inductor and at least one capacitor. The capacitor and / or the inductor can be implemented as passive components or as printed circuit elements. If space is limited, coupling via an excitation electrode can be achieved. The sensor electrode is part of this circuit and contributes capacitively to the overall system. The resonant circuit is excited by an excitation circuit at a defined frequency. The frequency is variably adjustable by the excitation circuit and is set by a control unit. A coupling circuit extracts the signal from the resonant circuit and feeds it to the control unit for evaluation.The housing wall, together with the sensor electrode, forms a coupling capacitance to the environment, whereby the maximum capacitance change that the sensor can experience is determined by this coupling capacitance.

[0021] The control unit evaluates the signal level of the extracted signal. A baseline is established within the control unit based on the extracted signal. Therefore, there is no fixed detection threshold, but rather a dynamic detection threshold, calculated as the baseline plus a threshold value. The sensor signal should be unaffected, or only minimally affected, by external environmental factors such as humidity, water accumulation, rain, snow, dirt deposits, etc., to ensure reliable and / or false-trigger-free operation.

[0022] As determined, the resonance curve of the resonant circuit shifts to lower frequencies under external capacitive loading, caused by approach or contact with a human limb. The detectable shift can be very small. The maximum shift of the resonance frequency can be to a frequency determined by a series connection of the coupling capacitance and the contact capacitance. Due to its small value, the coupling capacitance determines the maximum change.

[0023] As further investigations revealed, the resonance curve is damped under external resistive loading caused by external environmental influences. This means that the amplitude of the resonance frequency initially decreases without a shift in the resonance frequency itself. However, if the external resistance decreases, the resonance frequency shifts to lower frequencies, and the amplitude of the resonance frequency increases again. Furthermore, it was found that the change in signal amplitude in the branch of the resonance curve above the resonance frequency of the fundamental signal always occurs in smaller values. In contrast, in the branch of the resonance curve below the resonance frequency, the signal value or signal amplitude increases under purely capacitive loading, while the signal amplitude decreases under resistive loading due to the damping behavior and only increases again at low resistance values.

[0024] Therefore, using the branch of the resonance curve above the resonance frequency is not desirable. Instead, the branch of the resonance curve below the resonance frequency is chosen for the measurement. The resonant circuit is operated in steady state at a frequency Fmess1 below the resonance frequency, to be specified in more detail, in order to exhibit minimal sensitivity to external resistive loads.

[0025] In a further embodiment, the resonant circuit can be operated at at least two frequencies. One of these is the resonant frequency Fres of the undamped resonant circuit, and the other is the frequency Fmess1, which is lower by a defined amount. The signal change at the measurement frequency Fmess1 is then compared with the decrease at the resonant frequency Fres; that is, the delta values ​​for the signal amplitudes are compared. This allows even a small resistive load to be detected when the trigger threshold at frequency Fmess1 is exceeded, since the decrease at the resonant frequency Fres is then significantly greater.

[0026] In a further refinement, several closely spaced measurement frequencies can be considered. Specifically, measurements are taken at one frequency Fhilf1 or at two additional frequencies Fhilf1 and Fhilf2, very close to Fmess1. The changes in signal amplitude at these frequencies Fhilf1 and / or Fhilf2 must be comparable to those at the measurement frequency Fmess1. For example, a slight increase in the changes in signal amplitude is recorded under capacitive loading, whereas they fluctuate considerably under resistive loading, meaning they can be positive and / or negative under low-impedance loads.

[0027] Preferably, the following frequencies are chosen for operating the resonant circuit: - Fres: Resonance frequency of the unactuated sensor or resonance frequency of the actuated sensor for the maximum signal change. - Fmess1: Below the resonant frequency of the actuated sensor, specifically approximately 1% to 6% below the resonant frequency. - Fhilf1: Fmess1 - approx. 0.5% of Fmess1. - Fhilf2: Fmess1 + approx. 0.5% of Fmess1.

[0028] The invention provides a capacitive sensor that is insensitive to water and / or dirt, especially for applications in the exterior of vehicles.

[0029] The advantages achieved with the invention lie particularly in the fact that the switching element exhibits significantly improved immunity to environmental interference. For example, no false triggering of the sensor occurs up to a water and / or dirt resistance of 5 kΩ. Furthermore, the switching element achieves an improvement in its operational and / or functional reliability. Thus, the switching element can also be used for safety-critical applications, especially in the exterior of a motor vehicle.

[0030] An embodiment of the invention with various further developments and configurations is shown in the drawings and is described in more detail below. The drawings show... Fig. 1. A motor vehicle with a control element and a user located outside, shown in a schematic view. Fig. 2 the detailed design of the switching control element comprising an electrical resonant circuit Fig. 1, Fig. 3 the switching control element as in Fig. 2, wherein this is exposed to water and / or contaminants, Fig. 4. A diagram showing the progress of the [something] at the [something] in Fig. The measured values ​​determined for the 2 depicted resonant circuit as a function of the excitation frequency for the resonant circuit, Fig. 5 a diagram for the course of the at the in Fig. The measured values ​​determined for the 3 depicted resonant circuit as a function of the excitation frequency for the resonant circuit, Fig. 6. an excerpt from the diagram according to Fig. 5 in enlarged view, Fig. 7 according to Fig. 2 further detailed switching controls, and Fig. 8 the electrical equivalent circuit for the in Fig. 7 shown switching control elements.

[0031] In Fig. Figure 1 shows a motor vehicle 1 with a car door 3, which is to be opened by a user 2. The car door 3 has a door handle 4 with an actuating surface 6, whereby the user 2 triggers the opening of the car door 3 by touching 8 the actuating surface 6 with their hand 7. To detect the touch 8, a switching element 5 is located in the motor vehicle 1, specifically in the door handle 4 (see Figure 1). Fig. 2) ordered.

[0032] The in Fig. The control element 5, shown in more detail below, in the form of a control panel, includes the actuation surface 6 for manual operation by the human hand 7. Of course, instead of the human hand, another element 7, for example a pen or the like, can also be used for input. A capacitive sensor 9 interacts with the actuation surface 6 such that the sensor 9 generates a signal 10 when the element 7 approaches the actuation surface 6 and / or when the element 7 touches the actuation surface 6 and / or when pressure is applied to the actuation surface 6 by the element 7. The signal 10 is then used to switch and / or trigger a function in the form of a switching and / or control signal. In this case, the signal 10 is forwarded to a control unit (not shown) in the motor vehicle 1, whereupon the control unit opens the car door 3.

[0033] The capacitive sensor 9 comprises an electrical resonant circuit 11, a signal generator 12 for exciting the resonant circuit 11 with a first excitation frequency fmess1, a measuring unit 13 for measuring a measured value when the resonant circuit 11 is operating at the first excitation frequency fmess1, and an evaluation unit 14 for generating the signal 10. The measured value is the respective electrical voltage applied to the resonant circuit 11 and / or the electrical current flowing in the resonant circuit 11 during its operation. Upon a corresponding change in the measured value, the evaluation unit 14 detects the effect of the element 7 on the actuating surface 6 and then generates the signal 10. The evaluation unit 14 thus generates the signal 10 depending on the change in the measured value when the element 7 acts on the actuating surface 6.

[0034] The resonant circuit 11 is in turn formed by an electrical capacitor 15 and an inductor 16. In Fig. 4 is the course of the measured values ​​taken by measuring unit 13 for the in Fig. The resonant circuit 11 shown in Figure 2, in which the actuating surface 6 is ideally dry, is shown in more detail as a function of the excitation frequency fanr. The frequency in kHz is plotted on the abscissa and the measured value in unspecified digital units on the ordinate. As can be seen, the resonant circuit 11 has a resonance curve 30, which exhibits a resonance at approximately 2.92 MHz. The amplitude 40 is greatest for the measured value at the resonance point. If the actuating surface 6 is touched by the human hand 7 according to Fig. When a person acts on the resonant circuit 11, the total electrical capacitance acting on the circuit changes because the human hand 7 creates an additional capacitance 17. In addition to this additional capacitance 17, the hand 7 also possesses an electrical resistance 18, which, however, is extremely small and negligible without further influence. Due to the change in the capacitance acting on the resonant circuit 11, the resonance curve shifts depending on the strength of the contact with the actuating surface 6, specifically from resonance curve 31 for a light touch to resonance curve 32 for a stronger touch. As can be seen by comparing resonance curves 30, 31, and 32, the resonance frequency fres shifts to lower measured values, and the amplitudes 41 and 42 of the measured values ​​at the resonance point also decrease. Therefore, the change in the amplitudes 40, 41, and 42 at the resonance point is conventionally used to detect the touch.For example, signal 10 is generated when the difference 43 of the amplitudes 40, 41 or 42 exceeds a predetermined threshold.

[0035] However, if the actuation surface 6 is wet, the behavior of the resonant circuit 11 changes. As in Fig. As shown in more detail in Figure 3, the actuating surface 6 is wetted with water droplets 19. The water droplets 19 possess an electrically resistive component 20, which in turn significantly influences the oscillation behavior of the resonant circuit 11. Similarly, contaminants have a resistive component that influences the oscillation behavior; however, for the sake of simplicity, only water 19 will be considered in detail below.

[0036] In Fig. 5 shows the influence of water 19 on the actuation surface 6 in more detail. With a dry actuation surface 6, the effect already described in Fig. The resonance curve 30 shown in Figure 4 is present. When water 19 is applied to the actuating surface 6, the resonance curves shift to smaller amplitudes. With light wetting with water 19, resonance curve 33 is obtained; with slightly greater wetting, resonance curve 34; and with medium wetting, resonance curve 35. Finally, with heavy wetting, resonance curve 36 is obtained, and with extremely heavy wetting, for example by immersion in water 19, resonance curve 37 is obtained. Furthermore, with heavy wetting with water 19, the resonance point for resonance curves 36 and 37 shifts relative to resonance curve 30 for the dry actuating surface 6.As can be seen, even when the difference 44 between the amplitude 40 for the resonance curve 30 without the influence of water 19 and the amplitude 45 for the resonance curve 33 with slight wetting with water 19 is present, it is no longer possible to distinguish whether the actuating surface 6 is being touched or whether the actuating surface 6 is wetted with water 19. Rather, in such a case, the signal 10 may be generated incorrectly, which in turn leads to a malfunction of the switching element 5.

[0037] The invention has now yielded the insight of how to use the Fig. 5 recognizes that the left branch 38 of the resonance curves 33, 34, 35 with respect to the resonance point, when wetted with water 19, is essentially identical to the left branch 38 of the resonance curve 30 for the dry actuation surface 6. Thus, the presence of water 19 on the actuation surface 6 has no significant influence on the vibration behavior of the resonant circuit 11 with respect to the left branch 38, meaning that contact with the actuation surface 6 by hand 6 can be detected without having to fear the described malfunction. For the operation of the resonant circuit 11, the first excitation frequency fmess1 is selected on the left branch 38, such that the first excitation frequency fmess1 is lower than the resonance frequency fres of the resonant circuit 11. To reliably detect contact with the actuation surface 6, the evaluation unit 14 generates the signal 10 only if the difference 46 (see [reference to be added]) Fig. 6) The difference between the measured value at the first excitation frequency fmess1 on the resonance curve 31' upon contact of the actuating surface wetted with water 19 and the baseline measured value on the resonance curve 30 for the unaffected resonant circuit 11 at the first excitation frequency fmess1 exceeds a predetermined baseline threshold. "Unaffected resonant circuit" means that there is neither an effect of the element 7 on the actuating surface 6 nor is the actuating surface 6 wetted with water 19. "Resonance curve 31'" denotes the resonance curve of the resonant circuit 11 when the actuating surface 6 is wetted by the element 7.

[0038] The area around the first excitation frequency fmess1 on the left branch 38 from Fig. 5 is for a resonant circuit 11 with a quality factor for the L(coil 16) / C(capacitor 15) combination of approximately 8 in Fig. 6 shown enlarged. How to use the Fig. As can be seen in Figure 6, the coincidence of the resonance curves 30, 33, 34, 35 is particularly pronounced in an interval from fmess1' to fmess1'', where fmess1' lies approximately 6% and fmess1'' approximately 4% below the resonance frequency fres for resonance curve 30 at the unaffected actuating surface 6. To further increase the operational reliability of the switching element 5, it may therefore be advantageous to select the first excitation frequency fmess1 in a range of 6% to 4% below the resonance frequency fres. Preferably, the first excitation frequency fmess1 can be selected at approximately 5% below the resonance frequency fres.

[0039] How to continue the Fig. If the operating surface 6 is subjected to extremely heavy wetting, for example, if the vehicle 1 is exposed to a cloudburst under exceptional circumstances, the resonance curve 37 may deviate somewhat from the other resonance curves 30, 33, 34, 35, even in the interval from fmess1' to fmess1''. To prevent a malfunction of the switching control element 5 even in such an exceptional case, the signal generator 12 is designed to additionally excite the resonant circuit 11 with a further, second excitation frequency fmess2. It has proven advantageous that this further, second excitation frequency fmess2 corresponds approximately to the resonance frequency fres of the resonant circuit 11. The measuring unit 13 then measures a further, second measured value at this further, second excitation frequency fmess2.The evaluation unit 14 generates the signal 10 only if the difference 47 between the second measured value on the resonance curve 31' and the limit measured value on the resonance curve 30 for the again unaffected resonant circuit 11 at the second excitation frequency fmess2 falls below a predefined limit threshold. This allows a small resistive load on the resonant circuit 11 to be detected by the difference 46 even if the basic threshold is exceeded.

[0040] To further increase the fault tolerance of the switching control element 5, an additional plausibility check can be performed for the difference 46 exceeding the basic threshold. For this purpose, the signal generator 12 excites the resonant circuit 11 with at least one further third excitation frequency fmess3, which is close to the first excitation frequency fmess1. The measuring unit 13 then measures yet another, third measured value at this third excitation frequency fmess3. The evaluation unit 14 generates the signal 10 only if the difference 48 between this third measured value and the first measured value at the first excitation frequency fmess1 is small, in particular smaller than a predefined maximum value.

[0041] Advantageously, this plausibility check can verify whether the difference 48 between the third measured value and the first measured value is less than a predetermined maximum value. Only in this case is the signal 10 generated. A further improvement can be achieved by operating the resonant circuit 10 not only with a third excitation frequency fmess3 but with several third excitation frequencies fmess3, fmess3' that are close to the first excitation frequency fmess1. In particular, the third excitation frequency fmess3, fmess3' can be approximately ±0.1% to ±0.6% away from the first excitation frequency fmess1. Preferably, the third excitation frequency fmess3, fmess3' can be approximately ±0.3% to ±0.6% away from the first excitation frequency fmess1.The plausibility check described is based on the finding obtained by means of the invention that strongly fluctuating measured values ​​at further frequencies close to the first measuring frequency fmess1 indicate a resistive load on the resonant circuit 11 and thus the influence of water 19 on the actuating surface 6.

[0042] As already shown from the Fig. As explained in Figure 2, the resonant circuit 11 can comprise an inductor 16 and at least one capacitor 15. To accommodate the switching element 5 in small installation spaces, for example in the door handle 4, the capacitor 15 and / or the inductor 16 can be implemented as printed circuit components. Advantageously, the capacitor 15 and / or the inductor 16 can be arranged on a printed circuit board (not shown). As further explained in Fig. As can be seen in Figure 7, the actuating surface 6, in the form of a sensor electrode 50, can be a component of the capacitor 15, with an emitter electrode 51 connected to the signal generator 12 for exciting the resonant circuit 11 at the excitation frequencies 52 being a further component of the capacitor 15. A housing 53 with a housing wall 6 is provided for the switching control element 5. This housing wall then forms the actuating surface 6.

[0043] Furthermore, a control unit 54 is provided. The control unit 54 sets the respective excitation frequency 52 at the signal generator 12. A peak detector is provided as a measuring unit 13, which is connected to an analog-to-digital converter in the control unit 54, so that the measured values ​​are available in digital form to the evaluation unit 14, which is also formed by the control unit 54, for further processing. Preferably, the control unit 54 can be a microcontroller, a microprocessor, or the like. The signal generator 12 and / or the measuring unit 13 and / or the evaluation unit 14 can be hardware electronic circuits, but preferably they are implemented by software located in the control unit 54.

[0044] What's next in Fig. As shown in Figure 8, the capacitance 15 comprises, firstly, the capacitance 15' of the emitter electrode 51 as a coupling capacitance and, secondly, the capacitance 15" of the sensor electrode 50, which is formed by the housing wall as the actuating surface 6 in the manner of a coupling capacitance to the environment. Furthermore, the element 7 forms a further capacitance 17 when acting on the actuating surface 6. Finally, the water 19 wetting the actuating surface 6 forms an electrically resistive resistance 20. As further described in Fig. As shown schematically in Figure 1, a drive 55 is provided in the motor vehicle 1 for the movement of the car door 3. The switching and / or control signal 10 generated by the switching control element 5 then controls the drive 55 to open the car door 3.

[0045] The invention is not limited to the described and illustrated embodiments. Rather, it also encompasses all technically advanced developments within the scope of the invention defined by the claims. Thus, the switching element according to the invention can be used not only for opening car doors but also for moving a tailgate, a hood, or the like in a motor vehicle. Furthermore, the switching element can be used in conjunction with a drive for moving another type of locking element, for example, a door in a building. Finally, the switching element can also be used in control panels on household appliances, audio equipment, video equipment, telecommunications equipment, or the like. Reference symbol list 1 motor vehicle 2 users 3 car doors 4 door handles 5 Switching control element 6 Actuation surface / Housing wall 7. Hand (of the user) / Element 8 touch 9 capacitive sensors 10 Signal / switching and / or control signal 11 (electrical) resonant circuit 12 Signal generator 13 Unit of measurement 14 evaluation units 15 Capacitor (of resonant circuit) / Capacitance 15 Capacitance (of the emitter electrode) 15'' capacity (of the sensor electrode) 16 Inductance (of resonant circuit) 17 (additional) capacity (of the hand) 18 (electrical) resistance (of the hand) 19 water drops / water 20 (electrically resistive) resistance (of water) 30 Resonance curve (without contact) 31 Resonance curve (with light touch) 31' Resonance curve (with contact on wetted actuation surface) 32 Resonance curve (with stronger contact) 33 Resonance curve (with light wetting) 34 Resonance curve (with slightly greater wetting) 35 Resonance curve (at medium wetting) 36 Resonance curve (with heavy wetting) 37 Resonance curve (with extremely strong wetting) 38 left branch (of the resonance curve) 40 Amplitude (of measured value at the resonance point) 41 Amplitude (of measured value at the resonance point upon light touch) 42 Amplitude (of measured value at the resonance point with stronger contact) 43 Difference (for amplitudes with an unwetted actuation surface) 44 Difference (for amplitudes with wetted actuation surface) 45 Amplitude (of measured value at the resonance point with light wetting) 46 Difference (between measured values ​​on the resonance curve during actuation and the unaffected resonant circuit at the first excitation frequency) 47 Difference (between measured values ​​on the resonance curve during actuation and the unaffected resonant circuit at the second excitation frequency) 48 Difference (between measured values ​​on the resonance curve at the first excitation frequency and at the third excitation frequency, each upon activation) 50 Sensor electrode 51 Emitter electrode 52 Excitation frequency 53 cases 54 Control and / or monitoring unit 55 Drive

Claims

A switching control element, in particular for a motor vehicle (1), in the form of a control panel with an actuating surface (6) for manual operation by means of an element (7), wherein the element (7) is in particular a human hand, with a capacitively operating sensor (9) cooperating with the actuating surface (6) such that the sensor (9) generates a signal (10) when the element (7) approaches the actuating surface (6) and / or when the actuating surface (6) is touched by means of the element (7) and / or when pressure is applied to the actuating surface (6) by means of the element (7), and wherein the signal (10) serves to switch and / or trigger a function in the form of a switching and / or control signal, wherein the capacitively operating sensor (9) comprises an electrical resonant circuit (11), a signal generator (12) for exciting the resonant circuit with an excitation frequency (fmess1),A measuring unit (13) for measuring a measured value of the resonant circuit (11) at the excitation frequency (fmess1), in particular the electrical voltage applied to the resonant circuit (11) and / or the electrical current flowing in the resonant circuit (11), and an evaluation unit (14) for generating the signal (10) as a function of the change in the measured value when the element (7) acts on the actuating surface (6), characterized in that the excitation frequency (fmess1) is lower than the resonance frequency (fres) of the resonant circuit (11), in particular that the excitation frequency (fmess1) is selected in a range of approximately 6% to 4% below the resonance frequency (fres), preferably at approximately 5% below the resonance frequency (fres). Switching control element according to claim 1, characterized in that the evaluation unit (14) generates the signal only when the difference (46) between the measured value at the excitation frequency (fmess1) and the basic measured value for the unaffected resonant circuit at the excitation frequency (fmess1) exceeds a predetermined basic threshold. Switching control element according to claim 1 or 2, characterized in that the signal generator (12) excites the resonant circuit (11) with a further excitation frequency (fmess2), wherein in particular the further excitation frequency (fmess2) corresponds approximately to the resonance frequency (fres) of the resonant circuit (11), that the measuring unit (13) measures a further measured value at the further excitation frequency (fmess2), and that the evaluation unit (14) generates the signal (10) only if the difference (47) between the further measured value and the limit measured value for the unaffected resonant circuit (11) at the further excitation frequency (fmess2) falls below a predetermined limit threshold. Switching control element according to claim 1, 2 or 3, characterized in that the signal generator (12) excites the resonant circuit with at least one further excitation frequency (fmess3) located close to the excitation frequency (fmess1), in particular at a distance of approximately ±0.1% to ±0.6% from the excitation frequency (fmess1), preferably at a distance of approximately ±0.3% to ±0.6% from the excitation frequency (fmess1), that the measuring unit (13) measures a further measured value at the further excitation frequency (fmess3), and that the evaluation unit (14) generates the signal (10) only if the difference (48) between the further measured value and the measured value is small, in particular if the difference (48) is smaller than a predetermined maximum value. Switching control element according to one of claims 1 to 4, characterized in that the resonant circuit (11) comprises an inductor (16) and at least one capacitor (15), wherein in particular the capacitor (15) and / or the inductor (16) are formed as printed circuit components, that preferably the capacitor (15) and / or the inductor (16) are arranged on a printed circuit board, that further preferably the actuating surface (6) in the manner of a sensor electrode (50) is a component of the capacitor (15), that even more preferably a housing (53) with a housing wall (6) is provided, and that, once again more preferably, the housing wall (6) forms the actuating surface, in particular in the manner of a coupling capacitor to the environment. Switching control element according to one of claims 1 to 5, characterized in that a control and / or monitoring unit (54) is provided, that preferably the control and / or monitoring unit (54) sets the excitation frequency at the signal generator (12), that further preferably the evaluation unit (14) is formed by the control and / or monitoring unit (54), and that the control and / or monitoring unit (54) is more preferably a microcontroller, a microprocessor or the like. Switching control element according to one of claims 1 to 6, characterized in that a drive (55) is provided for the movement of a locking element, in particular for a door, such as a car door (3), a tailgate, a front hatch or the like of a motor vehicle (1), and that preferably the switching and / or control signal (10) controls the drive (55).

Images