Steering wheel grip sensor and grip detection method

Abstract

Steering wheel grip sensor, comprehensive: a controlled electrode that has a flat shape and extends along a rim of a steering wheel; a sensor electrode that has a flat shape and is located opposite the controlled electrode; a sine wave generator that supplies a sinusoidal voltage to the controlled electrode; a charge amplifier comprising a capacitive feedback element, detects a change in the amount of charge generated according to the capacitance of the sensor electrode, and outputs the change in the amount of charge as a change in voltage; a multiplication processor that multiplies the sine wave voltage by an output voltage of the charge amplifier; an integrator that smooths the result of multiplication by the multiplication processor using integration; and a grip detector that determines, according to a level of the smoothed result, whether the steering wheel is being gripped, wherein the sine wave generator receives a square wave signal and generates the sine voltage in synchronization with the square wave signal, the steering wheel handle sensor further includes a storage facility; a first analog-to-digital (AD) converter that performs an A / D conversion of the output voltage of the charge amplifier in synchronization with the square wave signal and stores a result of the A / D conversion as the first digital data in the memory; and a second A / C converter that performs an A / C conversion of the sine wave voltage from the sine wave generator in synchronization with the square wave signal and stores the result of the A / C conversion as second digital data in the memory, wherein the first A / D converter and the second A / D converter generate the first digital data and the second digital data respectively, wherein the first digital data and the second digital data each correspond to at least two cycles of a waveform of the sinusoidal voltage.

Description

[Technical field]

[0001] The present disclosure relates to a steering wheel handle sensor and a handle detection method for detecting the touch of a human hand on a steering wheel. [State of the art]

[0002] Patent Literature (PTL) 1 discloses a capacitive occupant detection system that detects the approach capability of a human body.

[0003] PTL 2 describes a capacitive sensing device comprising an antenna electrode for generating an alternating electric field in response to an alternating voltage induced in the antenna electrode, and a control and evaluation circuit configured to maintain the alternating voltage equal to a reference alternating voltage by injecting a current into the antenna electrode and to measure the current. The control and evaluation circuit includes a microcontroller with a digital output for providing a digital signal and a low-pass filter operatively connected to the digital output to generate the reference alternating voltage by low-pass filtering the digital signal.

[0004] PTL 3 describes a capacitive measuring system comprising several capacitive sensors and an evaluation circuit, wherein the capacitive sensors are supplied with a monofrequency voltage signal, wherein the output signals of the capacitive sensors are alternately connected to a synchronous rectifier via a multi-channel analog multiplexer, and wherein the signal gain of the output signals of the synchronous rectifier is calibratable depending on a switchable reference impedance, wherein the synchronous rectifier is implemented by a MOS semiconductor switch whose source-drain path forms a shunt controlled by the monofrequency voltage signal, and wherein at least one channel of the analog multiplexer is provided for transmitting a calibration signal generated by a reference voltage divider.

[0005] PTL 4 describes a capacitive occupant detection system comprising a sine wave signal generator for applying a sinusoidal voltage signal to an antenna electrode and a current sensing circuit for measuring current signals, based on which a control and evaluation unit determines and outputs an occupancy status. The signal generator is coupled to the antenna electrode via an amplitude adjustment stage, the amplitude adjustment stage being configured to match the amplitude of the sinusoidal voltage signal applied to the antenna electrode to an amplitude selected from at least two discrete amplitudes. The control and evaluation circuit selects one of the discrete amplitudes sequentially and causes the amplitude adjustment stage to adjust the amplitude of the voltage signal applied to the antenna electrode accordingly. The control and evaluation circuit performs an interference detection mode and an occupant detection mode.In interference detection mode, the current signals are measured while a smaller of at least two discrete amplitudes is selected, and it is determined whether the antenna electrode is subject to interference. In occupant detection mode, the current signals are measured while a larger of at least two discrete amplitudes is selected, and an occupancy status is determined based on the current signals thus measured. [Citation list][Patent literature] [PTL 1] US 7 656 169 B2 [PTL 2] DE 11 2014 001 890 T5 [PTL 3] DE 10 2018 000 884 A1 [PTL 4] DE 11 2011 100 443 T5 [Summary of the invention][Technical problem]

[0006] However, in PTL 1 there is a problem that the detection accuracy deteriorates due to a switching process depending on a control signal, a frequency change of a control signal and an influence of interference signals (noise).

[0007] In view of this, the present disclosure provides a steering wheel handle sensor and a handle detection method to reduce the deterioration of detection accuracy caused by frequency changes and the influence of interfering signals (noise) and to improve detection accuracy.

[0008] A steering wheel handle sensor according to one aspect of the present disclosure is a steering wheel handle sensor according to claim 1.

[0009] A grip detection method according to one aspect of the present disclosure is a grip detection method according to claim 18. [Advantageous effects of the invention]

[0010] A steering wheel handle sensor and a handle detection method according to the present disclosure reduce the deterioration of accuracy caused by frequency changes and the influence of interference signals, and improve detection accuracy. [Brief description of the drawings] Fig. Figure 1 shows an example of the interior of a vehicle in which a steering wheel handle sensor according to embodiment 1 is arranged. Fig. Figure 2 shows an example of attaching a steering wheel cover of the steering wheel handle sensor according to embodiment 1 to a rim. Fig. Figure 3 shows an example of a cross-sectional configuration of the steering wheel cover in embodiment 1. Fig. Figure 4 is a block diagram showing an example of a circuit configuration of the steering wheel handle sensor according to embodiment 1. Fig. Figure 5 is an explanatory diagram for the operation of a sensor according to a comparative example in comparison to the steering wheel handle sensor according to embodiment 1. Fig. Figure 6 is a block diagram showing an example of a circuit configuration of a steering wheel handle sensor according to embodiment 2. Fig. Figure 7 is an explanatory diagram for error detection in embodiment 2. Fig. Figure 8 shows different waveforms at the time of fault detection in embodiment 2. Fig. Figure 9 is a block diagram showing another example of a circuit configuration of the steering wheel handle sensor according to embodiment 1. Fig. Figure 10 is a block diagram showing an example of a circuit configuration of a steering wheel handle sensor according to embodiment 3. Fig. Figure 11 is a block diagram showing an example of a circuit configuration of a steering wheel handle sensor according to embodiment 4. Fig. Figure 12 shows an example of a correlation between the resistor Rx and the capacitor Cx of the steering wheel handle sensor according to embodiment 4. [Description of embodiments](knowledge underlying the present disclosure)

[0011] The inventors have determined that the capacitive occupant detection system according to PTL 1, which is specified in the "Prior Art" section, has the following problems.

[0012] Firstly, in PTL 1 a switching operation is required during the synchronous acquisition of a sensor signal, and therefore if the rise rate of the edge components of a control signal used to control the switching deteriorates, distortions and a acquisition phase shift occur in a signal that has undergone synchronous acquisition, leading to the problem of deteriorating acquisition accuracy.

[0013] Secondly, since the sensitivity of a sensor signal depends on the frequency of a sine wave, the problem is that the detection accuracy deteriorates when frequency changes occur in a drive signal.

[0014] Thirdly, the capacitive occupant detection system has the frequency characteristic that the level of a sensor signal increases with increasing frequency of a control signal, and thus the problem is that the detection accuracy deteriorates when the frequency of exogenous high-frequency interference signals is higher.

[0015] In view of this, the present disclosure provides a steering wheel handle sensor and a handle detection method to reduce the deterioration of accuracy caused, for example, by frequency changes and the influence of interference signals, and to improve detection accuracy.

[0016] To solve such problems, a steering wheel grip sensor, according to one aspect of the present disclosure, comprises: a driven electrode having a flat shape and extending along a rim of a steering wheel; a sensor electrode having a flat shape and located opposite the driven electrode; a sine wave generator supplying a sinusoidal voltage to the driven electrode; a charge amplifier comprising a capacitive feedback element, detecting a change in the amount of charge generated according to the capacitance of the sensor electrode, and outputting the change in the amount of charge as a change in voltage; a multiplication processor multiplying the sinusoidal voltage by an output voltage of the charge amplifier; and an integrator smoothing the result of the multiplication by means of integration by the multiplication processor.and a grip detector that determines, according to a level of the smoothed result, whether the steering wheel is being gripped;

[0017] Accordingly, for example, the degradation of accuracy due to frequency changes and the influence of interference signals can be reduced, and the detection accuracy improved. Firstly, the output voltage of the charge amplifier and the sine wave used as the drive signal are in phase, meaning they have no phase difference. Secondly, the multiplication processor detects the capacitance depending on whether the steering wheel is gripped, using product detection. Therefore, the switching process required in conventional technology is unnecessary, thus preventing phase shifting and signal distortion caused by switching, reducing the degradation of detection accuracy, and improving detection accuracy.Secondly, the sensitivity of the charge amplifier's output voltage does not depend on the frequency of the sinusoidal input signal, thus preventing any deterioration in detection accuracy even if the sinusoidal signal experiences a frequency shift. Thirdly, the magnitude of the charge amplifier's output voltage does not depend on the frequency of the sinusoidal input signal, thereby reducing the deterioration in detection accuracy caused by exogenous high-frequency interference.

[0018] The charge amplifier can comprise: a first input terminal that receives the sinusoidal voltage; a second input terminal that is connected to the sensor electrode; an output terminal; wherein the capacitive feedback element is connected between the output terminal and the second input terminal; and an operational amplifier that is connected to the first input terminal, the second input terminal and the output terminal, wherein the charge amplifier can supply the sinusoidal voltage output through the output terminal to the sensor electrode via the capacitive feedback element.

[0019] Accordingly, the charge amplifier incorporates a capacitive feedback element and thus outputs a change in the amount of charge generated in the sensor electrode as a change in voltage. The charge amplifier can be configured from a general-purpose operational amplifier with two input terminals and one output terminal, which reduces circuit costs.

[0020] In this case, the sine wave generator can receive a square wave signal and generate the sine voltage in synchronization with the square wave signal.

[0021] Accordingly, it is not necessary to include a quartz oscillator, thus reducing circuit costs.

[0022] In this case, the charge amplifier can include a low-pass filter connected in parallel to the capacitive feedback element, and the low-pass filter can allow a signal with a frequency lower than the frequency of the sinusoidal voltage to pass through.

[0023] Accordingly, the output voltage through the output terminal, which indicates the capacitance depending on whether the steering wheel is gripped, is in phase with the sine wave, while a signal indicating a resistance component, such as leakage through the output terminal, exhibits a 90-degree phase shift relative to the sine wave. Multiplication by the multiplication processor cancels out this latter signal, thus improving the disturbance and interference resistance properties.

[0024] The steering wheel grip sensor can further comprise: a memory; a first analog-to-digital (AD) converter that performs an ADC conversion of the charge amplifier's output voltage in synchronization with the square wave signal and stores the result of the ADC conversion as the first digital data in the memory; and a second ADC that performs an ADC conversion of the sine wave generator's voltage in synchronization with the square wave signal and stores the result of the ADC conversion as the second digital data in the memory. The multiplication processor can perform a process to average one waveform specified by the first digital data and one waveform specified by the second digital data, and then multiply the first averaged digital data by the second averaged digital data.

[0025] Accordingly, the A / D conversion and multiplication can be performed with extreme accuracy.

[0026] The steering wheel grip sensor can further comprise: a memory; a first analog-to-digital (AD) converter that performs an ADC conversion of the charge amplifier's output voltage in synchronization with the square wave signal and stores the result of the ADC conversion as the first digital data in the memory; and a second ADC that performs an ADC conversion of the sine wave generator's voltage in synchronization with the square wave signal and stores the result of the ADC conversion as the second digital data in the memory. The multiplication processor can multiply the first digital data by the second digital data and perform processing to average a waveform specified by the digital data resulting from the multiplication of the first digital data by the second digital data.

[0027] In comparison to the case where averaging is performed before multiplication, the amount of data stored in memory is therefore smaller and the computational effort can be reduced.

[0028] In this process, the square wave signal can be switched to one of at least three frequencies, whereby the first A / D converter and the second A / D converter can store the first digital data and the second digital data, respectively, in the memory for each of the at least three frequencies.

[0029] This avoids using first and second digital data corresponding to the frequency affected by interference, and allows the use of first and second digital data corresponding to a different frequency. Furthermore, a frequency-hopping spread spectrum technique can be employed to eliminate interference.

[0030] In this process, the first A / D converter and the second A / D converter can generate the first digital data and the second digital data respectively, where the first digital data and the second digital data each correspond to at least two cycles of a waveform of the sinusoidal voltage.

[0031] Accordingly, the acquisition accuracy can be improved compared to an A / D conversion performed in units of one cycle.

[0032] In this process, the first A / D converter and the second A / D converter can generate the first digital data and the second digital data, respectively, wherein the first digital data and the second digital data each correspond to at least three cycles of a sinusoidal voltage waveform, and the multiplication processor can compare sections of the first digital data that correspond to different ones of the at least three cycles of the waveform and discard one of the sections of the first digital data with the most distant value.

[0033] Accordingly, for example, a section of the digital data corresponding to a cycle that is affected by interference signals can be discarded, thereby improving the accuracy of the data acquisition.

[0034] In this process, the first A / D converter and the second A / D converter can generate the first digital data and the second digital data, respectively, wherein the first digital data and the second digital data each correspond to at least three cycles of a sinusoidal voltage waveform, and the multiplication processor can, for each of the at least three cycles of the waveform, calculate a mean and a deviation of a section of the first digital data corresponding to the cycle and discard the section of the first digital data corresponding to the cycle if the deviation is greater than or equal to a threshold value.

[0035] Accordingly, a section of the data corresponding to a cycle containing noise signals can be discarded, thereby increasing noise resistance and accuracy.

[0036] In this process, the multiplication processor can change the frequency of the square wave signal if a predetermined number of cycles, for which the deviation is greater than or equal to the threshold, occur in a continuous sequence.

[0037] Accordingly, if interference signals occur continuously, their influence can be reduced by changing the frequencies of a square wave signal and a sinusoidal voltage.

[0038] The steering wheel grip sensor may further comprise: a monitoring device that monitors whether a fault has occurred; and a damping switch that attenuates or amplifies the sinusoidal voltage. The monitoring device may have a normal monitoring mode in which the damping switch neither attenuates nor amplifies the sinusoidal voltage, and a temporary monitoring mode in which the damping switch attenuates or amplifies the sinusoidal voltage. In the normal monitoring mode, the monitoring device can monitor whether at least one short circuit of the driven electrode and / or a short circuit of the sensor electrode has occurred, and in the temporary monitoring mode, the monitoring device can monitor whether at least one break of the driven electrode and / or a break of the sensor electrode and / or a short circuit between the driven electrode and the sensor electrode has occurred.

[0039] The monitoring device can control a damping factor and a gain factor of the damping switch.

[0040] Accordingly, the performance of the steering wheel grip sensor can be determined by controlling a damping factor and a gain factor. Furthermore, a damping factor and a gain factor can be appropriately determined according to the variations of the individual steering wheel grip sensors.

[0041] The steering wheel grip sensor may further include: a correction device that performs correction processing to reduce a change in the amount of charge generated in the sensor electrode, wherein the change is caused by an environmental change. The multiplication processor may further: shift the phase of the charge amplifier's output voltage by 90 degrees; multiply the sinusoidal voltage by the shifted output voltage; and output the result of this multiplication to the correction device as an index of the environmental change.

[0042] If, for example, the resistance of an insulator covering the sensor electrode has the property of changing depending on the humidity, the detection accuracy can be improved by a correction processing to reduce this change.

[0043] The steering wheel grip sensor may further comprise: an additional charge amplifier, which includes a capacitive feedback element, detects a change in the amount of charge generated in the driven electrode, and outputs the change in charge as a change in voltage, wherein the change in charge is caused by an environmental change; and a correction device, which performs correction processing to reduce a change in the amount of charge generated in the driven electrode, wherein the change is caused by the environmental change. The multiplication processor may further: multiply the sinusoidal voltage by an output voltage of the additional charge amplifier; and output the result of the multiplication of the sinusoidal voltage by the output voltage to the correction device as an index (indication) of the environmental change.

[0044] If, for example, the capacitance of an insulator in contact with the controlled electrode has the property of changing depending on the humidity or temperature, the detection accuracy can be improved by a correction processing to reduce this change.

[0045] The steering wheel grip sensor can further comprise: a current amplifier, which includes a resistive feedback element and outputs a change in the current generated in the driven electrode as a change in voltage; and a correction device, which performs correction processing to reduce a change in the current generated in the driven electrode caused by an environmental change. The multiplication processor can further multiply the sinusoidal voltage by an output voltage of the current amplifier and output the result of the multiplication of the sinusoidal voltage by the output voltage to the correction device as an index of the environmental change.

[0046] If, for example, the resistance of an insulator in contact with the controlled electrode has the property of changing depending on the humidity or temperature, the detection accuracy can be improved by a correction processing to reduce this change.

[0047] The low-pass filter can include: a first resistive element; a second resistive element connected in series with the first resistive element; a first capacitive element connected to a junction point of the first resistive element and the second resistive element; and a third resistive element connected in series with the first capacitive element.

[0048] Accordingly, saturation can be prevented by limiting the gain of the charge amplifier. Furthermore, a third resistor is inserted so that the peak gain at a specific frequency (a cutoff frequency) can be attenuated.

[0049] The steering wheel grip sensor can further include: a charge supply circuit which, in a fault monitoring operating mode, supplies a predetermined amount of charge to the charge amplifier. The monitoring device can monitor whether the operation of the charge amplifier is normal, based on an output from the charge amplifier when no charge is supplied by the charge supply circuit, and on an output from the charge amplifier when charge is supplied by the charge supply circuit.

[0050] Accordingly, the monitoring device can monitor whether the operation of the charge amplifier is normal. Furthermore, the monitoring device can monitor whether the operation of the differential amplifier is normal.

[0051] The steering wheel grip sensor may further include: a variable resistor provided between ground and a connection point of the sensor electrode and the charge amplifier.

[0052] Accordingly, the variable resistance allows for correction to reduce changes (fluctuations) in operation caused by environmental changes affecting the steering wheel grip sensor, such as changes in temperature or humidity.

[0053] A grip detection method according to one aspect of the present disclosure is a grip detection method for use in a steering wheel grip sensor, comprising a driven electrode having a flat shape and extending along a rim of a steering wheel, and a sensor electrode having a flat shape and opposite the driven electrode, wherein the grip detection method comprises: supplying a sinusoidal voltage to the driven electrode; detecting a change in a charge quantity generated according to the capacitance of the sensor electrode by means of a charge amplifier comprising a capacitive feedback element; generating an output voltage by the charge amplifier that changes according to the change in the detected charge quantity; multiplying the sinusoidal voltage by the output voltage generated by the charge amplifier;Smoothing the result of multiplying the sine voltage by the output voltage by integration; and determining whether the steering wheel is gripped, according to a level of the smoothed result.

[0054] Accordingly, the deterioration of accuracy, for example due to frequency changes and the influence of interference signals, can be reduced, and the detection accuracy can be improved.

[0055] It should be noted that these general and specific aspects can be implemented using a system, a method, an integrated circuit, a computer program, a computer-readable recording medium such as a CD-ROM, or any combination of systems, methods, integrated circuits, computer programs, and recording media.

[0056] The following section describes embodiments in more detail with reference to the drawings.

[0057] It should be noted that the embodiments described below each provide a general or specific example. The numerical values, shapes, materials, elements, arrangement and connection of the elements, steps, and processing sequence of the steps described, for example, in the following embodiments are only examples and are therefore not intended to limit the present disclosure. [Version 1][ Appearance of the steering wheel grip sensor 100]

[0058] Fig. Figure 1 shows an example of an interior fitting of a vehicle 1 in which a steering wheel handle sensor 100 is arranged according to an embodiment.

[0059] As in Fig. As shown in Figure 1, the vehicle 1 comprises a steering wheel 3, a loudspeaker, and a display device, such as a liquid crystal display. The loudspeaker and the display device are configured, for example, as a warning device.

[0060] The steering wheel 3 imparts a steering angle to the vehicle 1. The steering wheel 3 comprises a rim 31, a spoke 32 which is essentially T-shaped and formed integrally with the inner circumference of the rim 31, and a horn switch cover that conceals a horn switch located in a central section of the spoke 32. The steering wheel grip sensor 100 comprises a steering wheel cover 110 and a control device 120.

[0061] Fig. Figure 2 shows an example of attaching the steering wheel cover 110 of the steering wheel handle sensor 100 according to embodiment 1 to the rim 31.

[0062] As in Fig. As shown in Figure 2, the steering wheel grip sensor 100 is a device that detects a grip and a touch by a user's hand (a human hand) on the steering wheel cover 110 and is arranged along the rim 31 of the vehicle 1. "Touch" means not only a state in which a user's hand is directly touching the steering wheel cover 110, but also a state in which the human hand is separated from the steering wheel cover 110, provided that the steering wheel grip sensor 100 can detect the human hand.

[0063] The steering wheel grip sensor 100 is a capacitive sensor that detects a user's grip on the steering wheel 3 in the vehicle 1. More precisely, the steering wheel grip sensor 100 detects whether a user's hand(s) is touching the steering wheel 3 by sensing a change in capacitance between the user's hand(s) and the steering wheel grip sensor 100. [Cross-sectional configuration of the steering wheel cover 110]

[0064] Fig. Figure 3 shows an example of a cross-sectional configuration of the steering wheel cover 110 in embodiment 1. The drawing is an enlarged schematic view of part of a cross-section taken in a stacking direction of the steering wheel cover 110 wrapped around the rim 31. As in Fig. As shown in Figure 3, the steering wheel cover 110 comprises an outer layer 11, a sensor electrode 112, a dielectric layer 12, a controlled electrode 113 and a urethane layer 13. The rim 31 is grounded to the metal body of the vehicle 1 (vehicle ground).

[0065] The outer layer 11 is made of an insulating material such as leather, imitation leather or synthetic resin.

[0066] It should be noted that the configuration of the steering wheel cover 110 is not limited to a configuration in which the outer layer 11, the sensor electrode 112, the dielectric layer 12, the driven electrode 113 and the urethane layer 13 are integrally wound around the rim 31, but can also be a configuration in which a detector, integrally comprising the sensor electrode 112, the dielectric layer 12 and the driven electrode 113, is wound onto a surface of the urethane layer 13 formed on the rim 31, with the outer layer 11 further being wound onto the surface of the detector.

[0067] The sensor electrode 112 is a flat electrode, formed, for example, from a mesh fabric woven from conductive fibers. The shape of the sensor electrode 112 can be a curved plate that is a section of a ring, a curved plate that is a section of a side face of a cylinder, or an accumulation of small flat surfaces. The sensor electrode 112 in Fig. 3 is a curved flat (planar) electrode corresponding to the whole or a section of a circular ring.

[0068] The controlled electrode 113 can have the same configuration as the sensor electrode 112, or it can have a different configuration, such as a configuration in which a metal conductor is sewn and attached to a surface of the dielectric layer 12.

[0069] The sensor electrode 112 and the driven electrode 113 are positioned opposite each other, with a dielectric layer 12 between them to form a capacitive element. The capacitance ΔC is added to the sensor electrode 112 in response to touch by the user's hand, as indicated by the dashed line in the figure. Fig. Figure 3 shows that the steering wheel handle sensor 100 detects whether a hand is touching by sensing a change in capacitance ΔC. [Steering wheel grip sensor 100 circuit configuration]

[0070] Fig. Figure 4 is a block diagram showing an example of a circuit configuration of the steering wheel handle sensor 100 according to embodiment 1. [Configuration of the steering wheel grip sensor 100]

[0071] Fig. Figure 4 is a block diagram showing an example of a circuit configuration of the control device 120 in the steering wheel grip sensor 100 according to embodiment 1. It should be noted that the sensor electrode 112 and the driven electrode 113 in the steering wheel cover 110 have been schematically added to the drawing.

[0072] The control device 120 in Fig. 4 comprises a sensor circuit 40 and a control processor 50.

[0073] The sensor circuit 40 includes a sensor connection T4, a control connection T5, a sine wave generator 41, a charge amplifier 44 and a differential amplifier 46.

[0074] Sensor terminal T4 is connected to sensor electrode 112 and the second input terminal I2 of the charge amplifier 44, and signals are simultaneously received from and output via sensor terminal T4. Specifically, a sinusoidal voltage fed back from the charge amplifier 44 is transmitted to sensor electrode 112 via sensor terminal T4. Simultaneously, a change in the amount of charge in response to a change in the capacitance of sensor electrode 112 is transmitted to the charge amplifier 44 via sensor terminal T4.

[0075] The control terminal T5 is connected to the controlled electrode 113 and the sine wave generator 41. A sine wave voltage as a control signal is transmitted from the sine wave generator 41 to the controlled electrode 113 via the control terminal T5.

[0076] The sine wave generator 41 receives a square wave signal from a control device 51, generates a sine wave voltage synchronized with the square wave signal, and supplies the sine wave voltage as a control signal to the driven electrode 113 via the control terminal T5. The square wave signal input from the control device 51 is, for example, a pulse width modulation (PWM) signal. It should be noted that in the present embodiment, the sine wave voltage supplied to the driven electrode 113 by the sine wave generator 41 can be a DC voltage (for example, 2 V) superimposed with a sine wave.

[0077] The charge amplifier 44 comprises a capacitive feedback element C11, detects a change in the amount of charge corresponding to the capacitance of the sensor electrode 112, and outputs the change in the amount of charge as a change in voltage. Accordingly, the charge amplifier 44 comprises a first input terminal I1, a second input terminal I2, an output terminal o1, a capacitive feedback element C11, an operational amplifier A11, resistors R11 and R12, and a capacitive element C12. The first input terminal I1 receives a sinusoidal voltage from the sine wave generator 41 and is connected to the non-inverting input terminal of the operational amplifier A11.

[0078] The second input terminal I2 is connected to the sensor terminal T4 and transmits a change in the amount of charge caused by a change in the capacitance of the sensor electrode 112 to the inverting input terminal of the operational amplifier A11.

[0079] A voltage corresponding to a change in the amount of charge, measured according to the capacitance of sensor electrode 112, is output via output terminal o1. For example, if the capacitance of sensor electrode 112 does not change, a sinusoidal voltage is output via output terminal o1 with the same phase and amplitude as a sinusoidal voltage applied through the first input terminal I1. Conversely, if the capacitance of sensor electrode 112 changes, a sinusoidal voltage with the same phase as the sinusoidal voltage applied through the first input terminal I1 and an amplitude corresponding to the change in capacitance is output via output terminal o1.

[0080] The capacitive feedback element C11 is connected between the output terminal o1 and the second input terminal I2 and feeds an output voltage applied via the output terminal o1 back to the second input terminal I2. The capacitive feedback element C11 functions to detect a change in the amount of charge caused by a change in the capacitance of the sensor electrode 112.

[0081] The operational amplifier A11 outputs a voltage to the second input terminal I2 through the capacitive feedback element C11, which eliminates the difference between the signals at the non-inverting input terminal and at the inverting input terminal.

[0082] The differential amplifier 46 amplifies the difference between a sinusoidal voltage from the sinusoidal wave generator 41 and an output voltage from the charge amplifier 44 and outputs the result of the amplification as a sensor signal through the analog-to-digital (AD) connection Ta to the analog-to-digital converter (ADC) 62.

[0083] A circuit comprising resistive elements R11 and R12 and capacitive element C12 forms a low-pass filter with a cutoff frequency lower than the frequency of a sinusoidal voltage. The low-pass filter is connected in parallel with the capacitive feedback element C11 and, at a frequency lower than the sinusoidal frequency, operates more dominantly than the capacitive element C11 to allow an output voltage applied via output terminal o1 to pass through and be fed back. Accordingly, the low-pass filter limits the gain of operational amplifier A11 to prevent gain saturation and reduces noise. Conversely, the operation of capacitive element C12 and resistive elements R11 and R12 prevents the output voltage from being fed back at a frequency higher than the cutoff frequency.Consequently, the capacitive element C11 operates dominantly to allow the output voltage applied to output terminal o1 to pass through. Thus, the low-pass filter limits the gain to prevent saturation at a frequency lower than the frequency of a sine wave and reduces a noise component. At a frequency higher than the frequency of a sine wave, the operational amplifier A11 switches to a charge gain determined solely by the capacitive element C11.

[0084] More precisely, the sensor electrode 112 is connected to ground via the resistor Rx, as shown in Fig. Figure 4 shows that resistor Rx exhibits a parasitic resistance due to a resistive component of the dielectric layer 12, which is located between the sensor electrode 112 and ground. As described above, when a sinusoidal voltage applied to the driven electrode 113 is a DC voltage with a superimposed sine wave, a DC current flows to ground through resistor Rx. If the resistivity of the dielectric layer 12 changes due to temperature or humidity variations, the value of the DC current flowing to ground through resistor Rx will also change. To reduce the influence of such a change in the DC component, the gain of operational amplifier A11 is limited to prevent saturation by using a low-pass filter with a cutoff frequency lower than the frequency of the sinusoidal voltage.

[0085] It should be noted that the low-pass filter comprises the series-connected resistors R11 and R12, as well as the capacitive element C12, which is connected between the non-inverting input terminal of the operational amplifier A11 and a junction of the resistors R11 and R12. Fig. 4 is provided, but in addition to the elements mentioned above, it may include a resistor R21 in series with the capacitive element C12, as shown in Fig. Figure 9 shows that by including resistor R21, the peak gain generated at a specific frequency (the cutoff frequency) can be reduced.

[0086] In Fig. The control processor 50 comprises the AD port Ta, the AD port Tb, the PWM port Tf, the control device 51, the multiplication processor 52, the integrator 54, the grip detector 56, and the memory 57. The multiplication processor 52 comprises the ADCs 62 and 63 and the multiplier 65. It should be noted that the control processor 50 can be implemented by a microcomputer or a microcontroller, which may include, for example, a central processing unit (CPU), the memory 57, the ADCs 62 and 63, the multiplier 65, and an input / output port. The memory 57 is a generic term for read-only memory (ROM), working memory (RAM), and electrically erasable flash memory. The functional block in Fig. 4 can be obtained by the CPU executing a program in memory 57. It should be noted that the multiplier 65 can be a hardware circuit, or part or all of the multiplier 65 can be obtained through software.

[0087] The first digital data 72, second digital data 73, and first multiplication data 67 are represented as data that are processed in the multiplication processor 52. Such data are temporarily stored, for example, in memory 57.

[0088] The AD connection Ta is connected to an output connection of the differential amplifier 46 and is used to input an analog signal into the ADC 62.

[0089] The AD connection Tb is connected to a terminal through which a sinusoidal voltage is output from the sinusoidal wave generator 41, and serves to input an analog sinusoidal voltage into the ADC 63.

[0090] The PWM connection Tf is connected to the control device 51 and the sine wave generator 41 and serves to transmit a square wave signal from the control device 51 to the sine wave generator 41. The square wave signal can be a PWM signal.

[0091] The control device 51 generates a square wave signal with a variable frequency and outputs the signal to the sine wave generator 41 via the PWM connection Tf. The control device 51 controls and instructs the ADCs 62 and 63 to obtain samples from an analog signal in synchronization with the square wave signal. The number of samples can be, for example, 16 samples per cycle of a sinusoidal voltage or sensor signal, or it can be 8 to 24 samples per cycle.

[0092] The multiplication processor 52 multiplies a sinusoidal voltage from the sine wave generator 41 by the output voltage of the charge amplifier 44. The sinusoidal voltage from the sine wave generator 41 is input via the A / D connection Tb. The output voltage of the charge amplifier 44 is input as a sensor signal via the differential amplifier 46 and the A / D connection Ta. The result of the multiplication corresponds to the capacitance of the sensor electrode 112, depending on whether the steering wheel is being gripped.

[0093] The ADC 62 performs an analog-to-digital conversion of a sampling signal from the differential amplifier 46, which is used as an output voltage from the charge amplifier 44, in synchronization with a square wave signal from the control device 51. The result of the analog-to-digital conversion is stored as the first digital data 72 in the memory 57. The first digital data 72 corresponds to the waveform of one or more cycles of the sensor signal. N can be 1, 2, 3, or more.

[0094] The ADC 63 performs an analog-to-digital conversion of a sinusoidal voltage from the sine wave generator 41 in synchronization with a square wave signal from the control device 51 and stores the result of the ADC conversion as second digital data 73 in the memory 57. The second digital data 73 corresponds to at least one N cycle or N cycles of the sinusoidal voltage. N is defined in the same way as described with respect to the first digital data 72.

[0095] The multiplier 65 multiplies the first digital data 72 with the second digital data 73 and stores the result of the multiplication in memory 57 as first multiplication data 67.

[0096] It should be noted that the multiplication processor 52 can perform the processing to average the waveform specified by the first digital data 72 and the waveform specified by the second digital data 73, multiply the averaged first digital data with the averaged second digital data, and use the result of the multiplication as the first multiplication data 67. At this point, the integrator 54 can perform the processing to average instead of the multiplication processor 52.

[0097] Alternatively, the multiplication processor 52 can multiply the first digital data 72 with the second digital data 73 and perform processing to average the waveform specified by the first multiplication data 67, which is the result of the multiplication. At this point, the integrator 54 can perform the averaging instead of the multiplication processor 52.

[0098] The integrator 54 performs an averaging, i.e., a smoothing, by integrating the result of the multiplication from the multiplication processor 52.

[0099] The grip detector 56 determines whether the steering wheel is being gripped based on the level of the smoothed result of the multiplication. The level of the smoothed result of the multiplication corresponds to the capacitance of the sensor electrode 112 and is, for example, higher when the steering wheel is being gripped than when it is not. The grip detector 56 can incorporate hysteresis when determining whether the steering wheel is being gripped. More precisely, the grip detector 56 determines that a state of not gripping the steering wheel changes to a state of gripping the steering wheel when the level of the smoothed result of the multiplication reaches or exceeds a first threshold value th1. Conversely, the grip detector 56 determines that a state of gripping the steering wheel changes to a state of not gripping the steering wheel when the level of the smoothed result of the multiplication reaches or falls below a second threshold value th2.Hysteresis may occur at this point if the first threshold th1 is greater than the second threshold th2. [Comparative description of the steering wheel grip sensor 100 and a comparison example]

[0100] Next, the steering wheel grip sensor 100 and a comparison example will be described in relation to each other.

[0101] Fig. Figure 5 is an explanatory diagram showing the operation of a sensor according to the comparative example and the steering wheel handle sensor 100 according to embodiment 1 in comparison to each other. The comparative example in Fig. Figure 5 shows a similar configuration based on the sensor according to PTL 1.

[0102] In the circuit configuration of the comparison example, a sensor electrode SE is connected to an inverting input terminal of an operational amplifier A41. A driven electrode DE is connected to a non-inverting input terminal and receives a sinusoidal voltage.

[0103] A current amplifier 47 comprises a resistive feedback element R, detects a current Δi flowing in response to a change ΔC in the capacitance of the sensor electrode SE, and outputs a voltage corresponding to the detected current. The current amplifier is thus a current-to-voltage converter that outputs a detected current as a voltage.

[0104] The "Mathematical Expression" column of the comparison example shows the output voltage V = R × Δi0. Δi0 denotes a feedback current flowing through the resistive feedback element R, and Δi0 is equal to Δi from the perspective of a virtual short circuit between the non-inverting input terminal and the inverting input terminal. The current Δi flowing in response to the change ΔC in the capacitance of the sensor electrode SE can be represented by Δi = ω × ΔC × v. Here, v denotes a sinusoidal voltage applied to the non-inverting input terminal and the driven electrode DE. The output voltage V of the current amplifier 47 can be represented by V = ω × (ΔC × v) × R. Here, ω = 2πf. f denotes the frequency of the sinusoidal voltage v. In the comparative example, the output voltage V is not only proportional to the capacitance ΔC, but also to the frequency f.

[0105] As the "Signal Waveform" column of the comparison example shows, the output voltage V has a phase shift of 90 degrees relative to the sinusoidal voltage v. The "Signal Waveform" column of the comparison example shows examples of two types of waveforms obtained through synchronous switching detection to capture a change in the resistance component and phase-switching detection to capture capacitance components. Both detection methods involve a switching operation.

[0106] This leads to the following problem for the comparison example. First, a switching operation is required when sensing the output voltage V, and therefore, if the rise rate of the edge components of a control signal used to control the switching deteriorates, distortion and a sensing phase shift occur in a signal that has undergone synchronous sensing, resulting in the problem of deteriorating sensing accuracy.

[0107] Secondly, the sensitivity of the output voltage V depends on the frequency f, and therefore the problem is that the detection accuracy deteriorates when frequency changes occur in a drive signal.

[0108] Thirdly, the comparison example has a frequency characteristic in which the output voltage V increases with increasing frequency f, and thus the problem is that the detection accuracy deteriorates with increasing frequency of exogenous high-frequency interference signals.

[0109] To address such problems, the charge amplifier 44 in the “implementation form” records in the column “circuit configuration” in Fig. 5 a change ΔQ in the amount of charge generated according to the capacitance ΔC of the sensor electrode 112, and outputs the change ΔQ in the amount of charge as a change in the output voltage V, as already described with reference to Fig. As described in section 4, ΔQ0 denotes a feedback charge that generates the capacitance of the capacitive feedback element C, and ΔQ0 is equal to ΔQ from the perspective of a virtual short circuit between the non-inverting input terminal and the inverting input terminal. The output voltage V of the charge amplifier 44 is represented by V = (ΔC / C) × v. C denotes the capacitance of the capacitive feedback element. The output voltage V is proportional to the capacitance ΔC and does not depend on the frequency f. As shown in the "Signal Waveform" column, the output voltage V and the sinusoidal voltage v have no phase difference and are therefore in phase. Accordingly, product detection is possible using the product of the output voltage V and the sinusoidal voltage v, instead of synchronous detection using a switching operation.The column "Signal waveform" shows first multiplication data 67 and second multiplication data 68 as examples for product detection. First multiplication data 67 indicates the result of multiplying the output voltage V by the sinusoidal voltage v and represents the capacitance ΔC of the sensor electrode 112. Second multiplication data 68 indicates the result of multiplying the sinusoidal voltage v by the waveform of the output voltage V with a phase shift of 90 degrees.

[0110] The steering wheel handle sensor 100 according to embodiment 1 solves the first problem mentioned above using product detection. Since the output voltage V of the charge amplifier 44 does not depend on the frequency of the sinusoidal voltage v, the second and third problems mentioned above are also solved.

[0111] As described above, the steering wheel grip sensor 100 according to embodiment 1 comprises: a driven electrode 113, which has a flat shape and extends along a rim of a steering wheel; a sensor electrode 112, which has a flat shape and is opposite the driven electrode 113; a sine wave generator 41, which supplies a sinusoidal voltage v to the driven electrode 113; a charge amplifier 44, which includes a capacitive feedback element C11, detects a change in the amount of charge generated according to the capacitance of the sensor electrode 112, and outputs the change in the amount of charge as a change in voltage; a multiplication processor 52, which multiplies a sinusoidal voltage v by the output voltage V of the charge amplifier 44; an integrator 54, which smooths the result of the multiplication by the multiplication processor 52 by means of integration;and a grip detector 56, which determines, according to a level of the smoothed result, whether the steering wheel is being gripped;

[0112] According to this configuration, a deterioration in accuracy, for example due to frequency changes and the influence of interference signals, can be reduced, thus improving the detection accuracy.

[0113] More precisely, firstly, the output voltage of the charge amplifier and the sine wave used as a drive signal are in phase, meaning they have no phase difference. Secondly, the multiplication processor detects the capacitance by product detection, depending on whether the steering wheel is gripped. Consequently, the switching operation required in conventional technology is unnecessary, thus reducing phase shift and signal distortion due to switching, minimizing the degradation of detection accuracy, and ultimately improving detection accuracy.

[0114] Secondly, since the sensitivity of the output voltage of the charge amplifier does not depend on the frequency of a sinusoidal voltage as the drive signal, even if frequency changes occur in a sinusoidal signal, a deterioration in the detection accuracy can be reduced.

[0115] Thirdly, the magnitude of the charge amplifier's output voltage does not depend on the frequency of the sinusoidal voltage used as the drive signal, thus reducing the deterioration of detection accuracy due to exogenous high-frequency interference signals.

[0116] It should be noted that in the Fig. 4 steering wheel handle sensor 100 shown, the control processor 50 can switch the square wave signal to one of at least three frequencies, and the ADC 62 and the ADC 63 can store the first digital data or the second digital data in memory 57 for each of the at least three frequencies.

[0117] This avoids using first and second digital data corresponding to the frequency affected by interference, and allows the use of first and second digital data corresponding to a different frequency. Furthermore, a frequency-hopping spread spectrum technique can be employed to eliminate interference.

[0118] The ADC 62 and the ADC 63 can generate the first digital data and the second digital data respectively, where the first digital data and the second digital data each correspond to at least two cycles of a waveform of the sinusoidal voltage.

[0119] Accordingly, the acquisition accuracy can be improved compared to an A / D conversion performed in units of one cycle.

[0120] It should be noted that the ADC 62 and the ADC 63 can generate the first digital data and the second digital data respectively, wherein the first digital data and the second digital data each correspond to at least three cycles of a sinusoidal voltage waveform, and the multiplication processor 52 can compare sections of the first digital data corresponding to different ones of the at least three cycles of the waveform, and can discard one of the sections of the first digital data with the most distant value.

[0121] Accordingly, a section of the digital data is used that corresponds to a different cycle than the cycle for which the value is furthest away, and thus, for example, a section of the digital data that is affected by interference signals can be discarded, and the acquisition accuracy can be improved.

[0122] The ADC 62 and the ADC 63 can generate the first digital data and the second digital data respectively, wherein the first digital data and the second digital data each correspond to at least three cycles of a sinusoidal voltage waveform, and the multiplication processor 52 can, for each of the at least three cycles of the waveform, calculate a mean and a deviation of a section of the first digital data corresponding to the cycle and discard the section of the first digital data corresponding to the cycle if the deviation is greater than or equal to a threshold value.

[0123] Accordingly, a section of the data corresponding to a cycle containing noise signals is discarded, thereby increasing noise resistance and accuracy.

[0124] The multiplication processor 52 can change the frequency of the square wave signal if a predetermined number of cycles, for which the deviation is greater than or equal to the threshold, occur in a continuous sequence.

[0125] Accordingly, if interference signals occur continuously, their influence can be reduced by changing the frequencies of a square wave signal and a sinusoidal voltage. [Version 2]

[0126] In addition to embodiment 1, embodiment 2 describes a configuration for performing correction processing to reduce operational changes caused by a change in the environment of the steering wheel handle sensor 100, and an error monitoring system to monitor whether the operation is normal.

[0127] More precisely, such an environmental change includes, for example, a change in the resistance of the outer layer 11 in Fig. 3, a change in the capacitance of the controlled electrode 113 in Fig. 3 and a change in the resistance of the urethane layer 13 in Fig. 3.

[0128] The resistance of the outer layer 11, for example, has temperature- or humidity-dependent properties, meaning it is dependent on the temperature and humidity at the outer layer 11. By utilizing such temperature- or humidity-dependent properties of the outer layer 11, the steering wheel grip sensor 100 detects changes in the resistance of the sensor electrode 112 and the outer layer 11, thus essentially detecting the temperature and humidity without a separate temperature or humidity sensor. The temperature and humidity properties can be corrected based on the detected resistance change. The term "temperature and humidity" here means either "both temperature and humidity" or "either temperature or humidity."This definition depends on the material of the outer layer 11.

[0129] Furthermore, the driven electrode 113 is located opposite the ring 31, with the urethane layer 13 positioned between them, or it is wound around the ring 31, with the urethane layer 13 positioned between them. Thus, the driven electrode 113 and the ring 31 form a capacitor. Since the ring 31 is grounded (connected to earth), the capacitor formed by the driven electrode 113 and the ring 31 has a specific capacitance. It should be noted that the capacitance varies depending on the temperature and humidity of the urethane layer 13. By utilizing such temperature- and humidity-dependent properties, the steering wheel grip sensor 100 detects the temperature and humidity at the driven electrode 113 and the urethane layer 13 by sensing the change in the capacitance of the driven electrode 113.Accordingly, properties that depend on temperature and humidity / humidity can be corrected even if no temperature or humidity / humidity sensor is present.

[0130] Fig. Figure 6 is a block diagram showing an example of a circuit configuration of the steering wheel grip sensor 100 according to embodiment 2. The in Fig. The configuration shown in 6 differs from the one in Fig. The configuration shown in Figure 4 is essentially modified by adding sensor connections T1 to T3, a damping switch 42, a charge amplifier 43, a multiplexer 45, a selection control connection Tc, an AD connection Td, an AD connection Te, a test (CHK) connection Tg, an output monitoring connection Th, an ADC 60, a clock generator 61, an ADC 64, third digital data 74, a multiplier 66, second multiplication data 68, third multiplication data 69, a fault monitoring device 53 and a correction device 55, and by adding a bandpass filter to the differential amplifier 46.

[0131] The following description focuses on different points, while redundant descriptions of the same points are omitted.

[0132] The sensor connections T1 to T4 connect four sensor electrodes 112 when four pairs, each with a sensor electrode 112 and a controlled electrode 113, are contained in the steering wheel cover 110.

[0133] The damping switch 42 switches between (i) damping or amplification of a sinusoidal voltage supplied by the sinusoidal wave generator 41 via the charge amplifier 43 to the controlled electrodes 113, and (ii) passing on the sinusoidal voltage without damping or amplification.

[0134] The charge amplifier 43 comprises the capacitive feedback element C21, detects a change in the amount of charge generated in the driven electrode 113 due to an environmental change, and outputs the change in the amount of charge as a change in voltage. Thus, the charge amplifier 43 comprises the capacitive feedback element C21, the operational amplifier A21, the resistors R21 and R22, and the capacitive element C12. The charge amplifier 43 is the same as the previously described charge amplifier 44. It should be noted that the steering wheel grip sensor 100 can also use the charge amplifier 43 instead of the one described in Fig. The current amplifier 47 shown in Figure 5 may be included. In this case, the current amplifier 47 detects a change in the current generated in the driven electrode 113 due to an environmental change and outputs the change in current as a change in voltage.

[0135] The multiplexer 45 selects one of the sensor connections T1 to T4 and connects the selected sensor connection to the second input connection I2 of the charge amplifier 44. This selection is made according to a selection control signal input by the control device 51 via the selection control connection Tc. It should be noted that the multiplexer 45 may not connect one of its four connections to another, but may have a configuration in which one of its M connections is connected to another. M can be an integer equal to 2, 3, 5, or more, and is an integer greater than the number of pairs, each comprising a sensor electrode 112 and a driven electrode 113.

[0136] It should be noted that the in Fig. The configuration shown in Figure 6 is one in which the driven electrodes 113 are contained in the pairs and are all electrically connected to each other. Thus, the driven electrodes 113 are connected to a single drive terminal T5. However, the configuration is not limited to the one above, and, for example, one of the driven electrodes 113 can be selected by a different multiplexer and connected to the drive terminal T5. In this case, the driven electrode 113 that is paired with the sensor electrode 112 selected by the multiplexer 45 can be selected by the other multiplexer.

[0137] The selection control port Tc is connected to a control port of the multiplexer 45 and receives a selection control signal output by the control device 51.

[0138] The AD connection Td is connected to an output terminal of the charge amplifier 43 and serves to input an analog signal into the ADC 64.

[0139] The AD connection Te is connected to the sine wave generator 41 and serves to input a sine voltage in the form of an analog signal into the ADC 60.

[0140] The CHK connection Tg serves to transmit a test signal from the fault monitoring device 53 to the damping switch 42. A test signal is a low-level signal in a normal monitoring mode, in which a sinusoidal voltage is not attenuated or amplified by the damping switch 42, and a high-level signal in a temporary monitoring mode, in which a sinusoidal voltage is attenuated or amplified.

[0141] The output monitoring terminal Th is used to forward an output signal from output terminal o1 to the fault monitoring device 53.

[0142] The ADC 60 performs an analog-to-digital conversion (ADC) of a sinusoidal voltage from the sine wave generator 41 and outputs the result of the ADC conversion to the clock generator 61. The use of the ADC result differs from that of the ADC 63. The ADC 60's result is used to generate a clock signal synchronized with the sinusoidal waveform. Accordingly, the ADC 60 performs sampling at a higher rate than the ADC 63.

[0143] The clock generator 61 produces a clock signal synchronized with the waveform of a sinusoidal voltage, based on the result of the analog-to-digital conversion by the ADC 60. Such a clock signal contains one or more sampling clock signals for the ADC 62 and the ADC 63. It should be noted that the clock generator 61 can produce a clock signal synchronized with a square wave signal (i.e., a PWM signal) from the control device 51. In this case, the ADC 60 need not be included.

[0144] The ADC 64 performs an A / D conversion of an output voltage of the charge amplifier 43 in synchronization with a clock signal of the clock generator 61 and stores the result of the A / D conversion as third digital data 74 in memory 57.

[0145] The third digital data 74 corresponds to the waveform of N cycles of an output voltage of the charge amplifier 43. Here, N is equal to the number of cycles of a signal contained in the first digital data 72.

[0146] The multiplier 65 multiplies the first digital data 72 with the second digital data 73 and stores the result of the multiplication as first multiplication data 67 in memory 57, similar to in Fig. 4. The first multiplication data 67 correspond to the capacitance ΔC of the sensor electrode 112.

[0147] In addition, the multiplier 65 shifts the phase of the waveform of the first digital data 72 by 90 degrees, multiplies the phase-shifted first digital data 72 with the second digital data 73 and stores the result of the multiplication as second multiplication data 68 in memory 57.

[0148] The second multiplication data 68 correspond to a resistance component that depends on a change in the environment of the sensor electrode 112, such as the temperature and humidity / humidity on the outer layer 11.

[0149] The multiplier 66 multiplies the second digital data 73 with the third digital data 74 and stores the result of the multiplication in memory 57 as third multiplication data 69.

[0150] The third multiplication data 69 correspond to the capacitance of the urethane layer 13, which changes depending on a change in the environment of the controlled electrode 113, such as the temperature and the humidity at the controlled electrode 113.

[0151] The correction device 55 performs a correction process to reduce deviations due to environmental changes, using second multiplication data 68 and third multiplication data 69 as indices (cues) for the environmental changes. For example, the correction device 55 corrects the thresholds th1 and th2 for detection by the grip detector 56 as a correction process. Furthermore, the correction device 55 can correct the level smoothed by the integrator 54 as a correction process. It should be noted that the correction device 55 can smooth the second multiplication data 68 and the third multiplication data 69 and use the smoothed second multiplication data 68 and the smoothed third multiplication data 69 as indices.

[0152] If the resistance of the outer layer 11, which acts as an insulator covering the sensor electrode 112, has the property of changing depending on temperature and humidity, correction processing can improve the detection accuracy by reducing this change. This example specifically includes a change in insulation resistance caused by the outer layer 11 being wetted with sweat from the hand(s) gripping the steering wheel, depending on the temperature. If the capacitance of the urethane layer 13, which acts as an insulator in contact with the driven electrode 113, has the property of changing depending on, for example, humidity or temperature, correction processing to reduce such changes can improve the detection accuracy.This example includes in particular a change in the permittivity of the urethane layer 13 caused by the absorption of moisture by the urethane layer 13, based on the temperature and humidity in the environment and the moisture of the steering wheel.

[0153] The fault monitoring device 53 has a normal monitoring mode, in which the damping switch 42 neither attenuates nor amplifies a sinusoidal voltage, and a temporary monitoring mode, in which the damping switch 42 attenuates and amplifies a sinusoidal voltage and determines whether a fault has occurred. In the normal monitoring mode, the fault monitoring device 53 determines whether at least one short circuit to ground of the driven electrode 113 and / or a short circuit to ground of the sensor electrode 112 has occurred. In the temporary monitoring mode, the fault monitoring device 53 determines whether at least one break of the driven electrode 113 and / or a break of the sensor electrode 112 and / or a short circuit between the driven electrode 113 and the sensor electrode 112 has occurred.It should be noted that a break in the driven electrode 113 comprises two types of breakage: a break in a cable connected to the driven electrode 113 and an electrode breakage due to a break in the flat driven electrode 113. A break in the sensor electrode 112 comprises two types of breakage: a break in a cable connected to the sensor electrode 112 and an electrode breakage due to a break in the flat sensor electrode 112. When the following description refers only to "breakage," it refers to both types of breakage.

[0154] Next, the fault detection by the fault monitoring device 53 is described.

[0155] Fig. Figure 7 is an explanatory diagram of the error detection in embodiment 2. Fig. Figure 8 shows different waveforms at the time of fault detection in embodiment 2.

[0156] The line in Fig. Figure 7 shows the types of faults detected during fault detection. The column indicates the signal change when a fault occurs and whether fault detection is possible in both the normal monitoring mode and the temporary monitoring mode, each of which is included in a fault monitoring mode. It should be noted that the normal monitoring mode is typically used to monitor whether a fault has occurred while the steering wheel grip sensor 100 is operating to detect a grip (a touch). The temporary monitoring mode is used to temporarily stop operation for grip detection and enter a state where it monitors whether a fault has occurred.

[0157] The fault monitoring device 53 determines whether the controlled electrode 113 has a break, a short circuit to ground, or a short circuit to the sensor electrode 112. It should be noted that the fault monitoring device 53 cannot determine which type of fault has occurred, i.e., whether it is a break, a short circuit to ground, or a short circuit to the sensor electrode 112.

[0158] The fault monitoring device 53 determines whether the sensor electrode 112 has a break, a short circuit to ground, or a short circuit to the controlled electrode 113. It should be noted that the fault monitoring device 53 cannot determine which type of fault has occurred, i.e., whether it is a break, a short circuit to ground, or a short circuit to the controlled electrode 113.

[0159] Fig. Figure 8 shows a CHK signal, the sinusoidal voltage v, the output of the charge amplifier 43 / 44, the output of the differential amplifier 46, and the output of the multiplication processor 52 (result of the multiplication). It should be noted that Fig. Figure 8 shows an example where the mode switches to temporary monitoring mode when the CHK signal is at a high level and the sinusoidal voltage v is attenuated.

[0160] The following will refer to the Fig. 7 and Fig. Eight specific examples of fault detections performed by the fault monitoring device 53 are described.

[0161] First, as in Fig. As shown in Figure 7, cable breaks of the sensor electrode 112 and the controlled electrode 113 are not detected in normal monitoring mode, and therefore the fault monitoring device 53 switches off, as shown in Figure 7. Fig. Figure 8 shows that during grip detection, the mode switches to temporary monitoring mode at predetermined intervals (for example, once every 0.3 seconds), as indicated by the CHK signal. The fault monitoring device 53 determines that a cable has a break if the output of the differential amplifier 46 in temporary monitoring mode exhibits a smaller amplitude change than the output in temporary monitoring mode under normal conditions.

[0162] It should be noted that the fault monitoring device 53 can detect that a cable has a break if, after acquiring the output (result of the multiplication) from the multiplication processor 52 in temporary monitoring mode instead of the output from the differential amplifier 46, the result of the multiplication is closer to A than the output in temporary monitoring mode under normal conditions. Here, A is defined as the result of the multiplication when no handling (touching) occurs in a normal state.

[0163] First, as in Fig. Figure 7 shows that electrode breaks of the sensor electrode 112 and the controlled electrode 113 are not detected in normal monitoring mode, and therefore the fault monitoring device 53 switches off during grip detection, as shown in Figure 7. Fig. Figure 8 shows that the device switches to temporary monitoring mode at predetermined intervals (for example, once every 0.3 seconds), as indicated by the CHK signal. The fault monitoring device 53 detects that an electrode has a break if the output of the differential amplifier 46 in temporary monitoring mode has a smaller amplitude than the output in temporary monitoring mode under normal conditions. A smaller amplitude means that the amplitude is reduced compared to the amplitude of the output from the differential amplifier 46 in temporary monitoring mode under normal conditions. The amount of the amplitude reduction varies depending on the location of a break caused by the failure of the sensor electrode 112 / the driven electrode 113, and the closer the broken section of the electrode is to a cable, the smaller the amplitude.

[0164] It should be noted that the fault monitoring device 53 can detect that an electrode has a break if, after acquiring the output (result of the multiplication) from the multiplication processor 52 instead of the differential amplifier 46 in temporary monitoring mode, the result of the multiplication shows a smaller value than the output (result of the multiplication) in temporary monitoring mode under normal conditions. Here, the amount of the reduction in the result of the multiplication varies depending on the location of a break caused by the break in the sensor electrode 112 / the driven electrode 113, and the closer the broken section of the electrode is to a cable, the smaller the result of the multiplication.

[0165] If next, as in Fig. As shown in Figure 7, it is determined whether the sensor electrode 112 and the controlled electrode 113 are short-circuited to ground; this can be detected in the normal monitoring mode, and thus, as in Fig. As shown in Figure 8, the fault monitoring device 53 determines, at the time of normal grip detection, whether the output of the charge amplifier 43 / 44 is lower than the output in a normal state. To improve the detection accuracy, the fault monitoring device 53 can, at this time, calculate the average of the outputs from the charge amplifiers 43 and 44 and determine that the sensor electrode 112 and the driven electrode 113 are short-circuited to ground if the average value is shifted to a lower value than that in the normal state.

[0166] It should be noted that a short circuit to ground can also be detected in temporary monitoring mode, and thus the fault monitoring device 53 can also determine in temporary monitoring mode whether a short circuit to ground has occurred.

[0167] Next, as in Fig. As shown in Figure 7, if the sensor electrode 112 and the controlled electrode 113 are short-circuited, this can be detected in the normal monitoring mode in a similar way to how a short circuit to ground is detected, and thus, as in Fig. As shown in Figure 8, the fault monitoring device 53 determines, at the time of normal grip detection, whether the output from the charge amplifier 43 or 44 is lower than the output in a normal state. To improve the detection accuracy, the fault monitoring device 53 can, at this time, calculate the average value of the output from the charge amplifier 43 or 44 and determine whether the sensor electrode 112 and the driven electrode 113 are short-circuited if the average value is shifted to a lower value than that in the normal state.

[0168] It should be noted that a short circuit between the sensor electrode 112 and the controlled electrode 113 can be detected in temporary monitoring mode, and thus the fault monitoring device 53 can also detect the occurrence of a short circuit between the sensor electrode 112 and the controlled electrode 113 in temporary monitoring mode.

[0169] Here, the symbols (*1) in the Fig. 7 and Fig. 8, that the detection in temporary monitoring mode is based on the output (sensor signal) of the differential amplifier 46. The symbols (*2) mean that the detection in both ordinary monitoring mode and temporary monitoring mode is based on the output (a sensor signal) of the charge amplifier 44, or the output (a driven signal) of the charge amplifier 43, or the average of the outputs, which is set when a fault occurs (in an abnormal state). The meaning of the detection indicated by (*1) is as follows. In ordinary monitoring mode, the level of the output (a sensor signal) of the differential amplifier 46 hardly changes when a fault occurs, and therefore fault detection is difficult.In contrast, the fault monitoring device 53 can easily perform fault detection in temporary monitoring mode by attenuating or amplifying a sinusoidal voltage, since the amplitude that the voltage should have (a level change) is smaller when a fault occurs (in the abnormal state). It should be noted that the output (result of the multiplication) of the multiplication processor 52 in temporary monitoring mode is also smaller when a fault occurs (in the abnormal state) than in the normal state, so the fault monitoring device 53 can perform fault detection based on the foregoing.

[0170] As described above, the steering wheel grip sensor 100 according to embodiment 2 further comprises: a fault monitoring device 53, which monitors whether a fault has occurred; and a damping switch 42, which attenuates or amplifies the sinusoidal voltage. The fault monitoring device 53 has a normal monitoring mode in which the damping switch 42 does not attenuate or amplify the sinusoidal voltage, and a temporary monitoring mode in which the damping switch 42 attenuates or amplifies the sinusoidal voltage.In normal monitoring mode, the fault monitoring device 53 monitors whether at least one short circuit to ground of the controlled electrode 113 and / or a short circuit to ground of the sensor electrode 112 has occurred, and in temporary monitoring mode, the fault monitoring device 53 monitors whether at least one break of the controlled electrode 113 and / or a break of the sensor electrode 112 and / or a short circuit between the controlled electrode 113 and the sensor electrode 112 has occurred.

[0171] In this case, the fault monitoring device 53 can control a damping factor and a gain factor of the damping switch 42.

[0172] Accordingly, the performance of the steering wheel grip sensor can be determined by controlling a damping factor and a gain factor. Furthermore, a damping factor and a gain factor can be appropriately determined according to the variations of the individual steering wheel grip sensors.

[0173] The steering wheel grip sensor 100 can further comprise: a correction device 55, which performs correction processing to reduce a change in the amount of charge generated in the sensor electrode 112, wherein the change is caused by an environmental change. The multiplication processor 52 can also: shift the phase of the output voltage of the charge amplifier 44 by 90 degrees; multiply the sinusoidal voltage by the shifted output voltage; and output the result of the multiplication of the sinusoidal voltage by the shifted output voltage to the correction device 55 as an index of the environmental change.

[0174] If, for example, the resistance of the outer layer 11, which is an insulator covering the sensor electrode 112, has the property of varying depending on temperature and humidity, the detection accuracy can be improved by a correction processing to reduce this variation.

[0175] The steering wheel grip sensor 100 can further comprise: an additional charge amplifier 43, which includes a capacitive feedback element C21, detects a change in the amount of charge generated in the driven electrode 113, and outputs the change in the amount of charge as a change in a voltage, wherein the change in the amount of charge is caused by an environmental change; and a correction device 55, which performs correction processing to reduce a change in the amount of charge generated in the driven electrode 113, wherein the change is caused by the environmental change. The multiplication processor 52 can further: multiply the sinusoidal voltage by an output voltage of the additional charge amplifier 43; and output a result of the multiplication of the sinusoidal voltage by the output voltage to the correction device 55 as an index of the environmental change.

[0176] If the capacitance of the urethane layer 13, which is an insulator in contact with the driven electrode 113, has the property of varying depending on moisture / humidity or temperature, the detection accuracy can be improved by a correction processing to reduce this variation.

[0177] The steering wheel grip sensor 100 can further comprise: a current amplifier 47, which includes a resistive feedback element R and outputs a change in a current generated in the driven electrode 113 as a change in voltage; and a correction device 55, which performs correction processing to reduce a change in the current generated in the driven electrode 113 caused by an environmental change. The multiplication processor 52 can further multiply the sinusoidal voltage by an output voltage of the current amplifier 47 and output the result of the multiplication of the sinusoidal voltage by the output voltage to the correction device 55 as an index of the environmental change.

[0178] If, for example, the resistance value of an insulator in contact with the controlled electrode 113 has the property of varying depending on humidity or temperature, the detection accuracy can be improved by a correction processing to reduce this variation. [Version 3]

[0179] Embodiment 3 describes a configuration for performing fault monitoring to monitor whether the operation of the charge amplifier 44 is normal and whether the operation of the differential amplifier 46 is normal.

[0180] Fig. Figure 10 is a block diagram showing an example of a circuit configuration of the steering wheel handle sensor 100 according to embodiment 3. Fig. 10 differs from Fig. 6 mainly by adding a charge supply circuit 48 and a CHK connector Ti.

[0181] The following description focuses on different points, while redundant descriptions of the same points are omitted.

[0182] The charge supply circuit 48 includes the switch S41, as well as the resistor R43 and the capacitor C41, which are connected in parallel.

[0183] One end of a parallel circuit comprising resistor R43 and capacitor C41 is connected to one end of switch S41. Another end of the parallel circuit is connected to a ground wire.

[0184] Switch S41 has one end connected to the end of the parallel circuit comprising resistor R43 and capacitor C41. Another end of switch S41 is connected to a line linking an output terminal of multiplexer 45 and the second input terminal I2 of charge amplifier 44. Switch S41 is turned on or off depending on a second test signal from the fault monitoring device 53. When switch S41 is turned on, an input value from charge amplifier 44 changes at the second input terminal I2. Note that the resistance value of resistor R43 and the capacitance of capacitor C41 are predetermined. This circuit configuration allows the charge supply circuit 48 to supply charge for testing in a fault monitoring operating mode.In fault monitoring mode, the charge supply circuit 48 supplies a predetermined amount of charge to the charge amplifier 44 via the second input terminal I2 by switching on switch S41. The predetermined amount of charge is determined in advance to ascertain whether the operation is normal and is calculated based on the resistance value of resistor R43 and the capacitance of capacitor C41.

[0185] The CHK terminal Ti serves to transmit a second test signal from the fault monitoring device 53 to the charge supply circuit 48. Under normal conditions, the second test signal has a low level and a high level when monitoring the operation of the charge amplifier 44. It should be noted that switch S41 is off when the second test signal has a low level and on when the second test signal has a high level.

[0186] It should be noted that when monitoring whether the operation of the charge amplifier 44 is normal and whether the operation of the differential amplifier 46 is normal, the multiplexer 45 may be connected to one of the sensor terminals T1 to T4 or may be in an off state in which the multiplexer 45 is not connected to any of the sensor terminals T1 to T4.

[0187] The fault monitoring device 53 monitors in fault monitoring mode whether the operation of the charge amplifier 44 and the differential amplifier 46 is normal.

[0188] First, the monitoring of the operation of the charge amplifier 44 by the fault monitoring device 53 is described.

[0189] It should be noted that the fault monitoring device 53 monitors whether the operation of the charge amplifier 44 and the differential amplifier 46 is normal when a user does not grip (hold) the steering wheel 3 (for example, when the ignition of the vehicle 1 is switched on or immediately after it has been detected that the user is not gripping the steering wheel 3).

[0190] First, the fault monitoring device 53 receives an output signal through the output terminal o1 via the output monitoring terminal Th when the second test signal is at a low level, or in other words, in a state where the switch S41 is off, and stores the output signal in the memory 57.

[0191] Next, the fault monitoring device 53 sets the second test signal to the high level to turn on switch S41 and receives an output signal through output terminal o1 in a state where switch S41 is turned on.

[0192] The fault monitoring device 53 calculates a change amount by comparing an output signal transmitted through output terminal o1 in a state where switch S41 is off and stored in memory 57 with an output signal transmitted through output terminal o1 in a state where switch S41 is on and stored in memory 57.

[0193] As described above, the resistance value of resistor R43 and the capacitance of capacitor C41 are predetermined, and thus the amount of change of the output signal transmitted through output terminal o1 when switch S41 changes from off to on can be predicted.

[0194] Accordingly, the fault monitoring device 53 compares the calculated change amount with the predicted change amount and determines that the operation of the charge amplifier 44 is normal if the calculated change amount differs from the predicted change amount by a predetermined amount or less, and determines that the operation of the charge amplifier 44 is abnormal if the calculated change amount differs from the predicted change amount by the predetermined amount or more.

[0195] Next, the monitoring of the operation of the differential amplifier 46 by the fault monitoring device 53 is described.

[0196] The fault monitoring device 53 monitors whether the operation of the differential amplifier 46 is normal when the fault monitoring device 53 determines that the operation of the charge amplifier 44 is normal.

[0197] First, the fault monitoring device 53 receives an output signal through an output terminal of the differential amplifier 46 via the AD terminal Ta when the second test signal is at a low level, or in other words, in a state where the switch S41 is off, and stores the output signal in the memory 57.

[0198] Next, the fault monitoring device 53 sets the second test signal to the high level to turn on switch S41 and receives an output signal through the output terminal of the differential amplifier 46 in a state in which switch S41 is turned on.

[0199] The fault monitoring device 53 calculates a change amount by comparing the output signal of the differential amplifier 46 stored in memory 57 in a state in which the switch S41 is off with the output signal of the differential amplifier 46 stored in memory 57 in a state in which the switch S41 is on.

[0200] As described above, the resistance value of resistor R43 and the capacitance of capacitor C41 are predetermined, and the operation of the charge amplifier 44 is normal, and thus the change in the output signal of the differential amplifier 46 can be predicted when the switch S41 changes from off to on.

[0201] Accordingly, the fault monitoring device 53 compares the calculated change amount with the predicted change amount, determines that the operation of the differential amplifier 46 is normal if the calculated change amount differs from the predicted change amount by a predetermined amount or less, and determines that the operation of the differential amplifier 46 is abnormal if the calculated change amount differs from the predicted change amount by the predetermined amount or more.

[0202] As described above, the steering wheel handle sensor 100 according to embodiment 3 also includes a charge supply circuit 48 and can monitor whether the operation of the charge amplifier 44 and the differential amplifier 46 is normal.

[0203] It should be noted that the present application is not limited to the embodiment 3 described above, and that the switch S41 can first be switched on and an output signal can be stored in the memory 57 through the output terminal o1 or from the differential amplifier 46, and afterwards the switch S41 can be switched off and an output signal can be received through the output terminal o1 or from the differential amplifier 46 and compared with the data of an output signal stored in the memory 57. [Version 4]

[0204] In addition to embodiment 2 or 3, embodiment 4 describes a configuration for performing correction processing to reduce operational changes caused by a change in the environment of the steering wheel handle sensor 100.

[0205] In embodiment 4, such an environmental change includes, in particular, a change in the resistance of the dielectric layer 12, a change in the capacitance of the sensor electrode 112, and a change in the resistance of the urethane layer 13, which may be caused, for example, by a change in temperature and / or humidity. Hereinafter, the term "temperature and humidity" means both temperature and humidity, or either temperature or humidity.

[0206] The sensor electrode 112 is wound around the ring 31, with the dielectric layer 12 positioned between them. The ring 31 is grounded, or in other words, the sensor electrode 112 is connected to ground, with a resistor Rx positioned between it and ground. The resistor Rx exhibits parasitic resistance based on a resistive component of the dielectric layer 12 located between the sensor electrode 112 and ground. The resistance Rx has temperature- and humidity-dependent properties.

[0207] The sensor electrode 112 is positioned opposite the ring 31, with, for example, a urethane layer 13 provided between them, or it is wound around the ring 31, with, for example, a urethane layer 13 provided between them. Thus, the sensor electrode 112 and the ring 31 form the capacitor Cx. Since the ring 31 is connected to ground, the capacitor Cx, which comprises the sensor electrode 112 and the ring 31, has a specific capacitance. It should be noted that the capacitance exhibits different properties depending on the temperature and humidity at the dielectric layer 12 and the urethane layer 13.

[0208] Here, the resistor Rx and the capacitor Cx exhibit a correlation. Preferably, for example, the dielectric layer 12 and the urethane layer 13 are configured such that the correlation (hereinafter referred to as the design-intended relationship) is such that it is less likely to impair the steering wheel grip sensor 100's determination of whether the steering wheel is being gripped, even if the resistance value of resistor Rx and the capacitance of capacitor Cx change depending on the temperature and humidity. However, there are cases in which the correlation between resistor Rx and capacitor Cx deviates significantly from the design-intended relationship, for example, due to variations in individual products or deterioration over time.

[0209] In the steering wheel grip sensor 100 according to embodiment 4, a correction process is performed to prevent the correlation between the resistor Rx and the capacitor Cx from deviating from the intended relationship, for example, due to variations in individual products or deterioration over time. Accordingly, changes in the operation of the steering wheel grip sensor 100 due to environmental changes can be reduced.

[0210] Fig. Figure 11 is a block diagram showing an example of a circuit configuration of the steering wheel handle sensor 100 according to embodiment 4. Fig. 11 differs from Fig. 10 mainly by adding a variable resistor Rv and a correction control connection Tk.

[0211] The following description focuses on different points, while redundant descriptions of the same points are omitted.

[0212] The variable resistor Rv is connected between a ground line (signal ground) and a line connecting the output terminal of the multiplexer 45 and the second input terminal I2 of the charge amplifier 44. The variable resistor Rv has a resistance value that changes depending on a correction control signal output by the correction device 55 through the correction control terminal Tk.

[0213] The correction control connection Tk is used to transmit a correction control signal from the correction device 55 to the variable resistor Rv.

[0214] The correction device 55 determines from the second multiplication data 68 and the third multiplication data 69 whether the correlation between the resistance Rx and the capacitor Cx deviates from the constructively intended relationship by a predetermined value or more.

[0215] More precisely, the correction device 55 performs the determination as follows. The second multiplication data 68 and the third multiplication data 69 are related to the resistance Rx and the capacitor Cx. Accordingly, for example, second multiplication data 68 and third multiplication data 69, which correspond to the intended relationship when the user does not touch the steering wheel 3, are stored for each degree of temperature and each degree of humidity.If (i) the current second multiplication data 68 and the current third multiplication data 69 are not in use while the user is not gripping the steering wheel 3, and (ii) the second multiplication data 68 and the third multiplication data 69 are not in use while the user is not gripping the steering wheel 3, under the same conditions as the current temperature and humidity / humidity, differ from each other by a predetermined value or more, a correlation between the resistor Rx and the capacitor Cx will be determined to be different by the predetermined value or more from the constructively intended relationship.

[0216] If the correlation between the resistor Rx and the capacitor Cx deviates from the intended relationship by the predetermined value or more, the correction device 55 performs a correction by changing the resistance value of the variable resistor Rv to bring the correlation between the resistor Rx and the capacitor Cx closer to the intended relationship.

[0217] In particular, if, for example, the resistance value of resistor Rx is small in relation to the capacitance of capacitor Cx and the correlation deviates from the constructively desired relationship, the correction device 55 transmits a correction control signal to the variable resistor Rv and increases the resistance value of the variable resistor Rv.

[0218] Here, the combined resistance Rs from the resistance Rx and the variable resistance Rv is represented by expression 1. [Math 1] Rs=Rx⋅RvRx+Rv=Rx1+Rx / Rv

[0219] It can be prevented that the correlation deviates from the constructively desired relationship by increasing the resistance value of the variable resistor Rv in order to bring the resistance value of the combined resistor Rs closer to the resistance value of the constructively desired relationship with respect to the capacitance of the capacitor Cx.

[0220] Similarly, if, for example, the resistance value of resistor Rx is large with respect to the capacitance of capacitor Cx and the correlation deviates from the constructively desired relationship, the correction device 55 transmits a correction control signal to the variable resistor Rv to reduce the resistance value of the variable resistor Rv in order to bring the resistance value of the combined resistor Rs close to the resistance value of the constructively desired relationship.

[0221] Fig. Figure 12 shows an example of a correlation between resistor Rx and capacitor Cx. The vertical axis shows the capacitance of capacitor Cx, and the horizontal axis shows the resistance value of resistor Rx or the combined resistor Rs. The solid line L0 indicates the intended relationship and shows, for example, a correlation in an initial state at the time of factory delivery or a correlation at a normal temperature. Dashed lines L1 and L2 indicate cases where the correlation between resistor Rx and capacitor Cx deviates significantly from the intended relationship, for example, due to variations between individual products or deterioration over time. The correction device 55 corrects the resistance value of the combined resistor Rs by increasing / decreasing the resistance value of the variable resistor Rv. As indicated by the arrows in Fig.As shown in Figure 12, the dashed lines L1 and L2, which deviate from the constructively desired relation, can be brought closer to the constructively desired relation indicated by the solid line L0.

[0222] Such a configuration enables correction processing to prevent the correlation between the resistor Rx and the capacitor Cx from deviating from the intended relationship due to variations in individual products or deterioration over time, and consequently, changes in the operation of the steering wheel grip sensor 100 caused by environmental changes can be reduced.

[0223] It should be noted that in the above embodiments, each element can be configured by dedicated hardware or obtained by executing a software program suitable for that element. Each element can be obtained by a program execution device such as a CPU or processor that reads and executes a software program stored on a recording medium such as a hard disk or semiconductor memory. The software that enables the updating of the steering wheel grip sensor according to the embodiments is a program as follows.

[0224] Thus, this program causes a computer to execute a grip detection method for use in a steering wheel grip sensor, comprising a driven electrode having a flat shape extending along a rim of a steering wheel, and a sensor electrode having a flat shape and opposite the driven electrode.The grip detection method comprises: applying a sinusoidal voltage to the driven electrode; detecting a change in the amount of charge generated according to the capacitance of the sensor electrode by a charge amplifier that includes a capacitive feedback element; generating an output voltage that changes according to the change in the detected amount of charge by the charge amplifier; multiplying the sinusoidal voltage by the output voltage generated by the charge amplifier; smoothing the result of the multiplication of the sinusoidal voltage by the output voltage by integration; and determining whether the steering wheel is being gripped according to a level of the smoothed result.

[0225] The foregoing is a description of the steering wheel grip sensor according to one or more aspects based on embodiments; however, the present disclosure is not limited to these embodiments. The scope of the one or more aspects of the present disclosure also includes embodiments resulting from the addition of various modifications to the embodiments that can be devised by those skilled in the art, as well as embodiments obtained by combining elements in different embodiments, provided that the resulting embodiments do not deviate from the inventive concept of the present disclosure. [Commercial Applicability]

[0226] The present disclosure relates to a steering wheel handle sensor that detects a person's grip on a steering wheel. [List of reference symbols] 41 Sine wave generator 42 damping switches 43, 44 Charge amplifier 48 Charge supply circuit 52 Multiplication processor 53 Fault monitoring device (monitoring device) 54 Integrator 56 Handle Investigators 57 storage 62 first AD converter 63 second AD converter 72 first digital data 73 second digital data 100 Steering wheel handle sensor 112 Sensor electrode 113 controlled electrode o1 Output port A11 Operational amplifier C11 capacitive feedback element I1 first input connection I2 second input connector R11 resistive feedback element RV variable resistance Rx resistance

Claims

[1] Steering wheel handle sensor, comprising: a controlled electrode that has a flat shape and extends along a rim of a steering wheel; a sensor electrode that has a flat shape and is located opposite the controlled electrode; a sine wave generator that supplies a sinusoidal voltage to the controlled electrode; a charge amplifier comprising a capacitive feedback element, detects a change in the amount of charge generated according to the capacitance of the sensor electrode, and outputs the change in the amount of charge as a change in voltage; a multiplication processor that multiplies the sine wave voltage by an output voltage of the charge amplifier; an integrator that smooths the result of multiplication by the multiplication processor using integration; and a grip detector that determines, according to a level of the smoothed result, whether the steering wheel is being gripped, wherein the sine wave generator receives a square wave signal and generates the sine voltage in synchronization with the square wave signal, the steering wheel handle sensor further includes a storage facility; a first analog-to-digital (AD) converter that performs an A / D conversion of the output voltage of the charge amplifier in synchronization with the square wave signal and stores a result of the A / D conversion as the first digital data in the memory; and a second A / D converter that performs an A / D conversion of the sine wave voltage from the sine wave generator in synchronization with the square wave signal and stores a result of the A / D conversion as second digital data in the memory, wherein the first A / D converter and the second A / D converter generate the first digital data and the second digital data respectively, wherein the first digital data and the second digital data each correspond to at least two cycles of a waveform of the sinusoidal voltage. [2] Steering wheel handle sensor according to claim 1, the charge amplifier includes: a first input terminal that receives the sine wave voltage; a second input terminal connected to the sensor electrode; an output port; wherein the capacitive feedback element is connected between the output terminal and the second input terminal; and an operational amplifier connected to the first input terminal, the second input terminal, and the output terminal, and wherein the charge amplifier supplies the sinusoidal voltage, which is output through the output terminal, to the sensor electrode via the capacitive feedback element. [3] Steering wheel handle sensor according to one of claims 1 and 2, wherein the charge amplifier includes a low-pass filter connected in parallel to the capacitive feedback element, and where the low-pass filter allows a signal with a frequency lower than the frequency of the sine wave to pass through. [4] Steering wheel handle sensor according to claim 1, further comprising: wherein the multiplication processor performs processing to average one waveform specified by the first digital data and one waveform specified by the second digital data, and multiplies the first averaged digital data with the second averaged digital data. [5] Steering wheel handle sensor according to claim 1, further comprising: wherein the multiplication processor multiplies the first digital data with the second digital data and performs processing to average a waveform specified by digital data resulting from the multiplication of the first digital data with the second digital data. [6] Steering wheel handle sensor according to claim 4 or 5, wherein the square wave signal is switched to one of at least three frequencies, and wherein the first A / D converter and the second A / D converter store the first digital data and the second digital data, respectively, in the memory for each of the at least three frequencies. [7] Steering wheel handle sensor according to one of claims 4 to 6, wherein the first A / D converter and the second A / D converter generate the first digital data and the second digital data respectively, wherein the first digital data and the second digital data each correspond to at least three cycles of a sinusoidal voltage waveform, and wherein the multiplication processor compares sections of the first digital data corresponding to different of at least three cycles of the waveform and discards one of the sections of the first digital data with the most distant value. [8] Steering wheel handle sensor according to one of claims 4 to 6, wherein the first A / D converter and the second A / D converter generate the first digital data and the second digital data respectively, wherein the first digital data and the second digital data each correspond to at least three cycles of a sinusoidal voltage waveform, and wherein the multiplication processor calculates for each of the at least three cycles of the waveform a mean and a deviation of a section of the first digital data corresponding to the cycle and discards the section of the first digital data corresponding to the cycle if the deviation is greater than or equal to a threshold. [9] Steering wheel handle sensor according to claim 8, wherein the multiplication processor changes a frequency of the square wave signal when a predetermined number of cycles for which the deviation is greater than or equal to the threshold occurs in a continuous sequence. [10] Steering wheel handle sensor according to any one of claims 1 to 9, further comprising: a monitoring device that monitors whether a fault has occurred; and a damping switch that dampens or amplifies the sine wave voltage, wherein the monitoring device has an ordinary monitoring mode in which the attenuator switch does not attenuate or amplify the sinusoidal voltage, and a temporary monitoring mode in which the attenuator switch attenuates or amplifies the sinusoidal voltage, wherein in normal monitoring mode the monitoring device monitors whether at least one short circuit to ground of the controlled electrode and / or a short circuit to ground of the sensor electrode has occurred, and wherein in temporary monitoring mode the monitoring device monitors whether at least one break of the driven electrode and / or a break of the sensor electrode and / or a short circuit between the driven electrode and the sensor electrode has occurred. [11] Steering wheel handle sensor according to claim 10, wherein the monitoring device controls a damping factor and a gain factor of the damping switch. [12] Steering wheel handle sensor according to any one of claims 1 to 11, further comprising: a correction device that performs correction processing to reduce a change in the amount of charge generated in the sensor electrode, wherein the change is caused by an environmental change, the multiplication processor furthermore: shifts the phase of the output voltage of the charge amplifier by 90 degrees; the sine wave voltage multiplied by the shifted output voltage; and outputs to the correction device as an index of environmental change, a result of multiplying the sinusoidal voltage by the shifted output voltage. [13] Steering wheel handle sensor according to any one of claims 1 to 11, further comprising: a further charge amplifier comprising a capacitive feedback element, detects a change in the amount of charge generated in the driven electrode and outputs the change in the amount of charge as a change in voltage, wherein the change in the amount of charge is caused by a change in the environment; and a correction device that performs correction processing to reduce a change in the amount of charge generated in the targeted electrode, wherein the change is caused by environmental changes, the multiplication processor furthermore: the sine wave voltage is multiplied by an output voltage of the further charge amplifier; and outputs to the correction device as an index of environmental change, a result of multiplying the sine voltage by the output voltage. [14] Steering wheel handle sensor according to any one of claims 1 to 11, further comprising: a current amplifier comprising a resistive feedback element and outputting a change in a current generated in the driven electrode as a change in voltage; and a correction device that performs correction processing to reduce a change in the current generated in the driven electrode, wherein the change is caused by an environmental change, wherein the multiplication processor further multiplies the sinusoidal voltage by an output voltage of the current amplifier and outputs a result of the multiplication of the sinusoidal voltage by the output voltage as an index of the environmental change to the correction device. [15] Steering wheel handle sensor according to claim 3, the low-pass filter includes: a first resistance element; a second resistive element connected in series with the first resistive element; a first capacitive element connected to a junction point of the first resistive element and the second resistive element; and a third resistive element connected in series with the first capacitive element. [16] Steering wheel handle sensor according to claim 10, further comprising: a charge supply circuit which, in an operating mode for fault monitoring, supplies a predetermined amount of charge to the charge amplifier, wherein the monitoring device monitors whether the operation of the charge amplifier is normal, based on an output of the charge amplifier when no charge is supplied by the charge supply circuit, and on an output of the charge amplifier when charge is supplied by the charge supply circuit. [17] Steering wheel handle sensor according to any one of claims 1 to 16, further comprising: a variable resistor that is provided between ground and a connection point of the sensor electrode and the charge amplifier. [18] Grip detection method for use in a steering wheel grip sensor comprising a driven electrode having a flat shape extending along a rim of a steering wheel and a sensor electrode having a flat shape and opposite the driven electrode, wherein the grip detection method comprises: Receiving a square wave signal and generating a sinusoidal voltage in synchronization with the square wave signal; Supplying the sinusoidal voltage to the controlled electrode; Detecting a change in the amount of charge generated according to the capacitance of the sensor electrode, by means of a charge amplifier that includes a capacitive feedback element; Generating an output voltage through the charge amplifier that changes according to the change in the detected amount of charge; Performing an analog-to-digital conversion of the charge amplifier's output voltage in synchronization with the square wave signal and storing the result of the analog-to-digital conversion as initial digital data in a memory; Performing an A / D conversion of the sine wave voltage in synchronization with the square wave signal, and storing the result of the A / D conversion as a second digital data point in the memory; Generating the first digital data and the second digital data, wherein the first digital data and the second digital data each correspond to at least two cycles of a waveform of the sinusoidal voltage; Multiply the sine wave voltage by the output voltage generated by the charge amplifier; Smoothing the result of multiplying the sine voltage by the output voltage using integration; and Determine whether the steering wheel is being gripped, according to a level of the smoothed result.

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