A kind of based on capacitive single electrode steering wheel off-hand detection implementation device

Abstract

This invention relates to the technical field of automotive electronics, and provides a device for realizing steering wheel hands-off detection based on a capacitive single-electrode sensor, comprising: a main control unit, a capacitive sensor, and a heating control circuit; wherein, the heating control circuit includes a steering wheel heating wire, which is reused as the sensing electrode of the capacitive sensor; the main control unit is electrically connected to the heating control circuit and controls the current of the steering wheel heating wire; the main control unit is electrically connected to the capacitive sensor and receives the capacitance change signal of the sensing electrode of the capacitive sensor; and, at the first moment when hands-off detection is activated, based on the capacitance change signal, it determines whether there is capacitance drift, adjusts the judgment threshold of hands-off detection, and shuts off the heating control circuit; at the second moment when hands-off detection is deactivated and a heating command is present, based on the capacitance change signal, it determines whether the real-time temperature has reached a preset temperature threshold, controls the heating control circuit to conduct to perform heating, and shuts off hands-off detection.

Description

Technical Field

[0001] This invention relates to the field of automotive electronics technology, and in particular to a device for detecting when a steering wheel is removed from its hands based on a capacitive single-electrode steering wheel. Background Technology

[0002] With the widespread adoption of Level 2 / Level 3 autonomous driving technology, drivers can temporarily free their hands in certain scenarios. However, to ensure safety, the system must be able to continuously monitor whether the driver is ready to take over vehicle control at any time. Therefore, reliable hands-off detection (HOD) functionality has become a critical safety requirement.

[0003] Currently, there are two main types of off-hand detection solutions:

[0004] Torque sensor solution: This is the earliest and lowest-cost solution. A torque sensor is installed on the steering column, typically a torsion bar connecting two magnetic rings. By measuring changes in magnetic flux, the torsional angle is precisely calculated, thus obtaining the torque value. When the driver grips the steering wheel with both hands and applies torque, the torsion bar undergoes a slight deformation, which the sensor detects. The system logic is very simple: if a persistent, minute torque above the noise threshold is detected, it is considered "hands on". If the torque signal disappears for an extended period or falls below the threshold, it is considered "hands off".

[0005] Capacitive sensing solution: This is currently the mainstream solution, where capacitive sensing electrodes are distributed inside the steering wheel rim. These electrodes are typically metal foil sheets or printed conductive ink / silver paste, wrapped under the steering leather and foam layers. An electrostatic field is formed between the electrodes and ground. When a person's hand approaches or touches the electrodes, it changes the capacitance value of this electric field. A dedicated capacitance-to-digital converter (CDC) chip measures the capacitance change of each electrode at extremely high frequencies and converts it into a digital signal.

[0006] In patent document CN113720361A, which discloses a steering wheel hands-off detection sensor with integrated heating function, a multiplexing sensing wire is proposed. This sensor controls the switching between acquisition and heating states. However, during prolonged use or when environmental changes cause capacitance drift, the hands-off detection becomes inaccurate. Furthermore, it relies on a single capacitance value for judgment, making it susceptible to momentary interference. Summary of the Invention

[0007] This application proposes a capacitive single-electrode steering wheel hands-off detection device to address the problems of torque sensor solutions being insensitive to slight hand grip, susceptible to interference, and having low reliability; multi-electrode capacitive sensing solutions being costly, difficult to wire, and complex to debug due to system complexity and a large number of electrodes; and in steering wheels with integrated heating functions, to achieve functional synergy between heating and touch detection, avoiding mutual interference and effectively overcoming the impact of environmental temperature drift on detection accuracy.

[0008] To achieve the above objectives, this application provides the following technical solution:

[0009] In a first aspect, this application proposes a device for detecting when a steering wheel is no longer in use based on a capacitive single-electrode steering wheel, comprising: a main control unit, a capacitive sensor, and a heating control circuit; wherein...

[0010] The heating control circuit includes a steering wheel heating wire, which is reused as the sensing electrode of a capacitive sensor. The main control unit is electrically connected to the heating control circuit and controls the current of the steering wheel heating wire.

[0011] The main control unit is electrically connected to the capacitive sensor and receives the capacitance change signal of the sensing electrode of the capacitive sensor.

[0012] Furthermore, at the very first moment of the off-hand detection activation, based on the capacitance change signal, it is determined whether there is capacitance drift, and the off-hand detection threshold is adjusted to shut off the heating control circuit.

[0013] At the second moment when the off-hand detection is off and a heating command is present, the system determines whether the real-time temperature has reached the preset temperature threshold based on the capacitance change signal, and controls the heating control circuit to turn on to execute heating, while turning off the off-hand detection.

[0014] In conjunction with the first aspect, the capacitive sensor is a capacitive-to-digital converter, which includes at least one touch detection channel and a reference channel.

[0015] The touch detection channel is electrically connected to the steering wheel heating wire, and the reference channel is electrically connected to the built-in fixed reference capacitor; the main control unit is used to monitor the capacitance value change of the reference channel and determine the capacitance drift value.

[0016] Additionally, the threshold for off-hand detection in the touch detection channel is adjusted based on the capacitance drift value.

[0017] In conjunction with the first aspect, the off-hand detection includes: comparing the real-time sampling value of the touch detection channel with the adjusted off-hand detection judgment threshold; if the real-time sampling value continuously exceeds the off-hand detection judgment threshold and reaches the preset de-shake time, it is determined that the hand is on the steering wheel.

[0018] In conjunction with the first aspect, the main control unit is also connected to a temperature acquisition circuit, which is used to acquire the ambient temperature in real time; wherein,

[0019] The temperature acquisition circuit includes a differential amplifier circuit, a multi-stage SAR ADC, and a temperature compensation unit. The input terminal of the differential amplifier circuit is electrically connected to the steering wheel heating wire, which is distributed in the steering wheel grip area. Each stage of the multi-stage SAR ADC is equipped with a residual sampling circuit and a residual amplification circuit to suppress PWM signal interference from the steering wheel heating wire.

[0020] The steering wheel heating wire is used to collect simulated ambient temperature signals from multiple monitoring points on the steering wheel.

[0021] The differential amplifier circuit is electrically connected to the output terminal of the steering wheel heating wire, and after noise suppression of the ambient temperature analog signal, it is input into the multi-stage SAR ADC to generate the ambient temperature digital signal.

[0022] The temperature compensation unit is electrically connected to the digital signal output terminal of the multi-stage SAR ADC, and performs dynamic temperature drift compensation on the ambient temperature digital signal by setting a first temperature drift threshold, and outputs the real-time temperature according to the dynamic temperature drift compensation; wherein, during dynamic temperature drift compensation, the front-stage SAR ADC of the multi-stage SAR ADC synchronously acquires the next temperature analog signal, realizing parallel processing of sampling and compensation.

[0023] In conjunction with the first aspect, the off-hand detection also includes:

[0024] Based on the steering wheel heating wires, the grip characteristics of the steering wheel are obtained, and a mathematical model of the capacitive signal is constructed to determine the real-time gesture characteristics; among which, the grip characteristics include grip area characteristics and grip position characteristics;

[0025] The maximum capacitance value corresponding to the driver's two-hand grip state and the minimum area threshold of the two-hand grip state are determined in advance by peak detection, and a gesture threshold model is constructed.

[0026] The real-time gesture features are input into the gesture threshold model. When the grip area features and grip position features corresponding to the real-time gesture features do not conform to the gesture threshold model, the steering wheel is in the off-hand state.

[0027] In conjunction with the first aspect, the heating control circuit includes a switching unit and a pulse width modulation unit, wherein the pulse width modulation unit is electrically connected to the control terminal of the switching unit; wherein,

[0028] The switching unit includes a high-side switch and a low-side switch, which are connected in series in the power supply circuits at both ends of the steering wheel heating wire. The main control unit controls the opening and closing of the high-side switch and the low-side switch to start and stop the heating function.

[0029] The pulse width modulation unit is used to generate a PWM signal with a target duty cycle during the second time period to drive the switching unit to intermittently heat the steering wheel heating wire. The PWM signal with the target duty cycle is determined based on the capacitance change signal so that the capacitance change interference is suppressed within the tolerance of the off-hand detection judgment threshold.

[0030] In conjunction with the first aspect, the main control unit is connected to a power management circuit, which includes an SBC chip and multiple output branches; wherein the SBC chip is connected to a successive approximation ADC module, an FIR digital filter, and a CAN protocol controller.

[0031] Successive approximation ADC modules are used to acquire differential voltage signals from multiple output branches;

[0032] FIR digital filters are used to convert differential voltage signals into continuous time series current dynamic curves to form a third-order polynomial fitting with real-time temperature as a correction coefficient, and to determine whether there is a power supply abnormality in the output branch.

[0033] In addition, when there is a power supply abnormality, the current dynamic curve of the output branch with the abnormal power supply is compared with the power supply template, so as to generate an abnormal message indicating the power supply deviation through the CAN protocol controller.

[0034] In conjunction with the first aspect, the input terminal of the power management circuit is connected to a reverse connection protection circuit; wherein, the reverse connection protection circuit is composed of a PMOS transistor, which is connected in series in the positive power input path to prevent damage to subsequent circuits due to reverse connection of the positive and negative terminals of the power supply.

[0035] In conjunction with the first aspect, the capacitive sensor includes a three-plate differential probe structure, an interface circuit, and a high-voltage excitation phase-sensitive demodulation module;

[0036] The interface circuit includes a charge amplifier, which is electrically connected to the steering wheel heating wire;

[0037] The three-plate differential probe structure includes an upper plate, a lower plate, and an interface electrode. The interface electrode is electrically connected to the interface circuit and determines the capacitance change signal through the upper and lower plates. The upper and lower plates are fixed transmitting electrodes, and a movable mass plate is set between the upper and lower plates.

[0038] The output terminal of the triode differential probe structure is electrically connected to the high-voltage excitation phase-sensitive demodulation module;

[0039] The high-voltage excitation phase-sensitive demodulation module converts the capacitance change signal into a driving voltage signal that adjusts the judgment threshold for off-hand detection through sinusoidal high-voltage excitation and phase-sensitive demodulation; the output of the high-voltage excitation phase-sensitive demodulation module is connected to a multi-stage SAR ADC.

[0040] In conjunction with the first aspect, the capacitor drift further includes the following adjustment steps:

[0041] The capacitance change signal is determined by the temperature acquisition circuit;

[0042] The capacitance change signal is filtered by the SBC chip to generate a capacitance dynamic curve. The capacitance drift is calculated by comparing the real-time capacitance dynamic curve with the preset target capacitance curve.

[0043] Based on the capacitance drift, a PWM signal with a compensating duty cycle is generated. When the capacitance drift is positive, the PWM signal duty cycle is reduced, and when the capacitance drift is negative, the PWM signal duty cycle is increased, so that the real-time capacitance is stabilized within the target capacitance threshold range.

[0044] The beneficial effects of this invention are as follows:

[0045] This invention uses capacitance drift detection and active dynamic threshold adjustment to actively and dynamically compensate for capacitance baseline shifts caused by temperature changes, environmental interference, or long-term aging, preventing misjudgments or missed judgments of the hand-held state due to drift, and also eliminating passive accuracy loss.

[0046] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0047] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0048] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof.

[0049] In the attached diagram:

[0050] Figure 1 This is a core architecture diagram of the device for detecting hands off the steering wheel based on a capacitive single-electrode capacitor, as described in this embodiment of the invention.

[0051] Figure 2 This is a system block diagram of the device for detecting when a steering wheel is off-hand using a capacitive single-electrode steering wheel, as described in an embodiment of the present invention.

[0052] Figure 3 This is a diagram showing the composition of the temperature acquisition circuit in an embodiment of the present invention;

[0053] Figure 4 This is a process diagram of off-hand detection in an embodiment of the present invention;

[0054] Figure 5 This is a diagram illustrating the steps for adjusting capacitor drift in an embodiment of the present invention. Detailed Implementation

[0055] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0056] Steering wheel off-hand detection uses sensors to monitor in real time whether the driver's hands are effectively gripping the steering wheel, ensuring the driver can take over vehicle control at any time while driving. In existing technologies, to achieve thinner and lower-cost sensors, a single sensing wire is reused to achieve off-hand detection and heating functions. However, capacitive sensing relies on changes in the capacitance of the sensing wire, and capacitance is significantly affected by temperature. The dielectric constant, geometry, and temperature characteristics of the surrounding medium all change with temperature, causing baseline capacitance drift.

[0057] To address the aforementioned technical deficiencies, this application proposes a device for detecting when a steering wheel is no longer in use, based on a capacitive single-electrode steering wheel. Figure 2 As shown, it includes: reverse connection protection circuit, power management circuit, main control unit, capacitive sensor, heating control circuit and temperature acquisition circuit; the reverse connection protection circuit is composed of PMOS transistors, which are connected in series in the positive power input path to prevent damage to the subsequent circuit due to the reverse connection of the positive and negative terminals of the power supply.

[0058] The power management circuit, centered on the System Basis Chip (SBC) and working with peripheral circuits, converts the maximum 42V input voltage into two stable 5V outputs to power the MCU and capacitive sensors respectively. The SBC also integrates a CAN transceiver for CAN communication between the MCU and the host computer. The main control unit uses a microcontroller to control system operation, process steering wheel touch data collected by the capacitive sensors and temperature acquisition circuit data, and control the heating control circuit according to instructions. The capacitive sensors periodically detect the steering wheel touch status and transmit the data to the MCU. The steering wheel heating wire also serves as the capacitive sensing electrode, achieving hardware multiplexing. The heating control circuit includes a high-side switch and a low-side switch, connected to both ends of the heating wire, which are switched on and off under MCU control to achieve the heating function. The temperature acquisition circuit monitors the system temperature in real time and transmits the data to the MCU. The MCU is configured to execute the following control flow: After the system powers on, it initializes each functional module; after initialization, it controls the capacitive sensor to periodically detect the steering wheel touch status. If there is a touch, it sends a signal to the host computer via CAN communication; if a heating command is received from the host computer, it uses a time-division multiplexing method to coordinate the control of heating and touch detection functions: it controls the high-side and low-side switches to be turned on, starts the heating process, and pauses touch detection; when heating reaches the set time or the temperature acquisition circuit feedback that the system temperature has reached the predetermined threshold, it controls the high-side and low-side switches to be turned off, stops heating, and re-enables the touch detection function; this process is repeated cyclically; the capacitive sensor uses a capacitance-to-digital converter (CDC) that supports multi-channel detection and has a built-in reference capacitor. The detection baseline is dynamically adjusted through the reference capacitor to overcome capacitance drift caused by changes in ambient temperature.

[0059] Example 1: As Figure 1 As shown, this application proposes a device for detecting steering wheel hands-off operation based on a capacitive single-electrode sensor, comprising: a main control unit, a capacitive sensor, and a heating control circuit; wherein,

[0060] The heating control circuit includes a steering wheel heating wire, which is reused as the sensing electrode of a capacitive sensor. The main control unit is electrically connected to the heating control circuit and controls the current of the steering wheel heating wire.

[0061] The main control unit is electrically connected to the capacitive sensor and receives the capacitance change signal of the sensing electrode of the capacitive sensor.

[0062] Furthermore, at the very first moment of the off-hand detection activation, based on the capacitance change signal, it is determined whether there is capacitance drift, and the off-hand detection threshold is adjusted to shut off the heating control circuit.

[0063] At the second moment when the off-hand detection is off and a heating command is present, the system determines whether the real-time temperature has reached the preset temperature threshold based on the capacitance change signal, and controls the heating control circuit to turn on to execute heating, while turning off the off-hand detection.

[0064] In the embodiments of this application, the main control unit is the control core, the capacitive sensor realizes the hands-off detection, and the heating control circuit realizes the steering wheel heating. Exemplarily, the main control unit is a microcontroller, microprocessor, and application-specific integrated circuit (ASIC). It is electrically connected to the heating control circuit and the capacitive sensor through GPIO and ADC interfaces, and performs signal acquisition, threshold adjustment, and circuit switching control under pre-implanted embedded software or firmware. Exemplarily, the main control unit determines whether there is capacitance drift based on the capacitance change signal, and then outputs an instruction to adjust the hands-off detection threshold.

[0065] In the embodiments of this application, a capacitive sensor is used for proximity detection and touch detection when the driver's hand is removed from the steering wheel. The steering wheel heating wire is reused as the sensing electrode of the capacitive sensor. Changes in the capacitance of the steering wheel heating wire are mapped to changes in the sensing electrode. When the driver's hand approaches or leaves the steering wheel, the capacitance between the electrode and the hand changes, and the capacitive sensor converts this capacitance change into an electrical signal output. In this application, the steering wheel heating wire serves as both a contact sensing sensor for hand removal detection and a heating component for steering wheel heating. The steering wheel heating wire is made of copper or a heatable alloy sensitive to capacitance changes, reducing the cost of the capacitor required by the capacitive sensor and saving internal space in the steering wheel.

[0066] In the embodiments of this application, the heating control circuit is used to control the heating of the steering wheel. Specifically, the temperature of the steering wheel heating wire is adjusted by controlling the current on and off and the voltage. The main control unit can turn on or off the current that heats the steering wheel heating wire by driving the switching components, and can also adjust the current magnitude and switch state to control the heating function, so as to improve the driver's comfort and experience through heating.

[0067] In the embodiments of this application, the capacitance change signal is an analog signal or a digital signal, which is read by the main control unit and analyzed by the built-in algorithm to realize hands-off detection and temperature determination, thereby realizing two modes: hands-off detection and steering wheel heating.

[0068] In the embodiments of this application, when the hands-off detection mode is activated, i.e., at the first moment, the main control unit performs the following steps: detecting capacitance drift based on capacitance change signals; identifying the capacitance change value corresponding to the drift phenomenon using a calibration algorithm built into the main control unit, employing moving average and adaptive filtering; and then adjusting the baseline change corresponding to the capacitance drift to achieve compensation. Because the steering wheel heating changes the electrode temperature, the electromagnetic environment also changes accordingly. Therefore, when dynamically adjusting the hands-off detection threshold, the heating control circuit is shut off to prevent detection errors.

[0069] In the embodiments of this application, when the off-hand detection is turned off and a heating command is received, i.e., at the second moment, the main control unit performs the following steps: based on the capacitance change signal, it infers the real-time temperature change and compares it with a preset heating temperature threshold to achieve temperature control. At this time, the off-hand detection is turned off to avoid signal conflict. The division between the first and second moments can prevent performance degradation caused by simultaneous heating and detection.

[0070] The beneficial effects of this application are as follows:

[0071] This application proactively compensates for capacitance baseline shifts caused by temperature changes, environmental interference, or long-term aging due to capacitance variations through capacitance drift detection and active dynamic threshold adjustment. This prevents false or missed detections of the hand-off state due to drift, and avoids passive accuracy loss. It also reduces the number of components, lowers costs and interference, while improving detection accuracy and system reliability. Specifically, it overcomes capacitance drift, avoids the impact of heating on detection, and achieves synchronous function multiplexing and intelligent control. When hand-off detection is initiated, this application determines capacitance drift, adjusts the judgment threshold, and shuts off the heating control circuit. When heating is initiated, it uses the capacitance change signal to determine the temperature, controls heating, and shuts off hand-off detection. These two different commands operate independently and do not interfere with each other.

[0072] Example 2: The capacitive sensor is a capacitive-to-digital converter, which includes at least one touch detection channel and one reference channel;

[0073] The touch detection channel is electrically connected to the steering wheel heating wire, and the reference channel is electrically connected to the built-in fixed reference capacitor; the main control unit is used to monitor the capacitance value change of the reference channel and determine the capacitance drift value.

[0074] Additionally, the threshold for off-hand detection in the touch detection channel is adjusted based on the capacitance drift value.

[0075] In the embodiments of this application, the touch detection channel is used to collect the steering wheel grip signal when the driver is driving, and the reference channel provides a stable reference capacitance; the two channels are compared to distinguish between real touch signals and drift interference. For example, in the case of a single channel, it is impossible to determine whether the capacitance change is caused by drift or hand contact.

[0076] In the embodiments of this application, the touch detection channel is electrically connected to the steering wheel heating wire, so that the touch detection channel can collect capacitance change signals through the reused heating wire to achieve hand-off detection.

[0077] In the embodiments of this application, the reference channel is electrically connected to a built-in fixed reference capacitor. The fixed reference capacitor is configured with a reference capacitance value that is unaffected by environmental interference and is used as a reference for drift detection: if the capacitance change trends of the touch channel and the reference channel are consistent (for example, both increase with increasing temperature), it is determined to be drift; if only the touch channel changes, it is determined to be actual hand contact. Without a fixed reference capacitor, there is no reference benchmark, and drift cannot be detected.

[0078] In the embodiments of this application, the main control unit is used to monitor the capacitance value change of the reference channel, determine the capacitance drift value, and then determine the drift compensation data. By comparing the real-time capacitance difference between the touch detection channel and the reference channel, the common drift amount caused by environmental factors is calculated. The common drift amount is used to characterize that the capacitance of both channels increases synchronously when the temperature rises, while the real-time capacitance difference remains basically unchanged. If the real-time capacitance difference changes abnormally, it indicates hand contact. Without this monitoring step, the degree of drift cannot be quantified.

[0079] In the embodiments of this application, adjusting the off-hand detection threshold of the touch detection channel based on the capacitance drift value is a drift compensation process. The threshold is dynamically adjusted up or down according to the determined drift value to ensure that the off-hand / handshake judgment criteria always match the current environment. Without adjusting the threshold, drift can lead to misjudgments; for example, if the baseline capacitance exceeds the original threshold after drift, it may be misjudged as a continuous handshake.

[0080] In the embodiments of this application, the capacitive sensor is a capacitance-to-digital converter to achieve high-precision acquisition of capacitance change signals; in optional embodiments, an analog capacitance sensor can also be used in conjunction with an independent ADC to achieve digital acquisition and dual-channel comparison of capacitance signals.

[0081] In the embodiments of this application, the capacitance change value obtained by comparing the touch detection channel and the reference channel, after dynamic threshold adjustment, not only solves the drift problem but also the interference problem. For example, when electromagnetic interference caused by the vehicle radar causes instantaneous fluctuations in the capacitance of the touch detection channel, the fixed capacitor connected to the reference channel remains unaffected. The main control unit can stably determine that the changing capacitance signal is interference rather than a real touch, thus reducing the false judgment rate.

[0082] The beneficial effects of this application are:

[0083] This application distinguishes between common environmental drift and real touch signals by comparing a reference channel with a fixed reference capacitor, avoiding the problems of misjudging drift as touch or missing real touch due to drift in traditional single-channel detection. Although touch detection channels and reference channels have been proposed in the prior art, this application ensures that the reference is not affected by external environmental interference from the steering wheel by incorporating a built-in fixed reference capacitor. With dynamic threshold adjustment and time-division control, the reference channel sampling and threshold update are completed quickly during the heating-detection switching interval, ensuring that compensation delay does not affect the real-time performance of the detection.

[0084] Example 3:

[0085] The off-hand detection includes: comparing the real-time sampling value of the touch detection channel with the adjusted off-hand detection judgment threshold. If the real-time sampling value continuously exceeds the off-hand detection judgment threshold and reaches the preset de-shake time, it is determined that the hand is on the steering wheel.

[0086] In the embodiments of this application, the drift compensation output, real-time sampled value, and adjusted threshold are compared when determining the hand-off detection threshold before steering wheel hand-off detection is performed. The main control unit continuously acquires the capacitance digital sampled value of the touch detection channel and compares it with the detection threshold adjusted by drift compensation. In this process, the real-time capacitance value is obtained through ADC sampling and compared with the dynamically adjusted threshold in the digital domain to determine the hand contact state, resulting in a more accurate judgment. Determining if the real-time sampled value continuously exceeds the hand-off detection threshold prevents errors caused by momentary judgments and continuously indicates the duration of the error. During the determination process, the real-time sampled value is greater than the set judgment threshold for multiple consecutive sampling cycles. Continuous judgment logic is adopted to avoid the randomness of single sampling, and multi-cycle verification ensures detection reliability.

[0087] In the embodiments of this application, the debouncing time corresponds to a sustained time standard, ensuring that a sampled value is consistently higher than a threshold within a set time period before being considered a valid signal. This effectively filters out high-frequency noise and mechanical vibration. The debouncing time is set by establishing a fixed or configurable time window; only when the signal continuously meets the conditions within this time window can it be considered a valid detection. Eliminating signal jitter through time-domain filtering is typically implemented using a counter or timer mechanism. In practical implementation, this can suppress signal fluctuations caused by mechanical vibration, electromagnetic interference, etc., preventing false triggering.

[0088] The beneficial effects of this application are:

[0089] This application addresses the baseline issue caused by drift by adjusting the dynamic threshold. Through continuous hands-off detection and de-jitter time, it employs a dual time-domain filtering approach, improving detection reliability in complex automotive environments. Combined with adaptive threshold adjustment, this forms a complete optimization system from signal acquisition to final judgment, preventing interference signals and enhancing the anti-interference capability of drift compensation.

[0090] Example 4: Figure 3 As shown, the main control unit is also connected to a temperature acquisition circuit, which is used to acquire the ambient temperature in real time; wherein,

[0091] The temperature acquisition circuit includes a differential amplifier circuit, a multi-stage SAR ADC, and a temperature compensation unit. The input terminal of the differential amplifier circuit is electrically connected to the steering wheel heating wire, which is distributed in the steering wheel grip area. Each stage of the multi-stage SAR ADC is equipped with a residual sampling circuit and a residual amplification circuit to suppress PWM signal interference from the steering wheel heating wire.

[0092] The steering wheel heating wire is used to collect simulated ambient temperature signals from multiple monitoring points on the steering wheel.

[0093] The differential amplifier circuit is electrically connected to the output terminal of the steering wheel heating wire, and after noise suppression of the ambient temperature analog signal, it is input into the multi-stage SAR ADC to generate the ambient temperature digital signal.

[0094] The temperature compensation unit is electrically connected to the digital signal output terminal of the multi-stage SAR ADC, and performs dynamic temperature drift compensation on the ambient temperature digital signal by setting a first temperature drift threshold, and outputs the real-time temperature according to the dynamic temperature drift compensation; wherein, during dynamic temperature drift compensation, the front-stage SAR ADC of the multi-stage SAR ADC synchronously acquires the next temperature analog signal, realizing parallel processing of sampling and compensation.

[0095] In the embodiments of this application, the temperature acquisition circuit determines the specific capacitance change value of capacitor drift by using the temperature signal in the actual environment. The temperature acquisition circuit continuously monitors the ambient temperature parameters around the steering wheel and periodically samples and acquires temperature data based on the thermistor effect or the temperature resistance characteristic.

[0096] In the embodiments of this application, a differential amplifier circuit suppresses noise, a multi-stage SAR ADC achieves high-precision analog-to-digital conversion, and a temperature compensation unit eliminates temperature drift errors. The distributed distribution of the steering wheel heating wires among the three components ensures that different gripping areas of the steering wheel are at the same temperature gradient, preventing single-point detection and thus avoiding deviations. An analog signal processing circuit employing a differential amplifier structure amplifies the voltage difference between the two input terminals, suppresses common-mode noise, improves the signal-to-noise ratio, eliminates common-mode interference, and enhances small-signal detection capabilities. The multi-stage SAR ADC is a multi-stage successive approximation register-type analog-to-digital converter that converts analog signals into digital signals through multi-stage comparison and digital approximation, with each stage processing bits to improve conversion accuracy and speed. The temperature compensation unit is a functional module for temperature error compensation, correcting measured values ​​based on a preset algorithm to compensate for temperature drift of the sensor and the circuit itself. The input of the differential amplifier is directly connected to the heating wire, which is reused as a temperature sensor. Utilizing the resistance-temperature characteristics of the heating wire, temperature changes are converted into voltage signals, enabling multiplexing and reducing costs. The heating wires are distributed to cover the main grip areas of the steering wheel, achieving distributed multi-point temperature monitoring and acquiring temperature distribution information. This temperature distribution information can be used to determine whether the hand grip on the steering wheel is correct. The residual signal amplifier amplifies the residual error from the previous stage, enhancing small signal detection capabilities and improving dynamic range.

[0097] In the embodiments of this application, the steering wheel heating wire can be controlled to heat via a PWM signal, thereby achieving duty cycle adjustment. High-frequency noise from the PWM signal can be coupled into the temperature acquisition signal. A residual sampling and amplification circuit can perform residual conversion in the front stage and residual amplification in the back stage to improve the PWM interference suppression ratio. The residual processing circuit suppresses high-frequency noise generated by the PWM switch through sampling timing control and signal processing, reducing the impact of PWM interference on temperature measurement. Multiplexing the heating wire as a multi-point temperature sensor network, time-division multiplexing the resistance change signals at different points, enables spatial temperature distribution monitoring without the need for additional sensors. An amplifier is directly connected to the signal output of the heating wire to amplify the weak sensing signal and improve signal quality. The signal is sent to the ADC after differential amplification and noise suppression. The differential structure suppresses common-mode noise, and the filter circuit eliminates interference in specific frequency bands. The ADC outputs digitized temperature data. The compensation unit receives the digital output of the ADC, acquires the raw temperature data through a digital interface, performs digital signal processing, and achieves temperature compensation in the digital domain.

[0098] In the embodiments of this application, the temperature simulation signal is susceptible to electromagnetic interference. Therefore, this application uses differential input and common-mode rejection to filter out common-mode noise, so that the ADC signal is free from interference signals.

[0099] In the embodiments of this application, the temperature acquisition circuit exhibits temperature drift. A preset first temperature drift threshold is used to perform secondary calibration on the acquired values, thereby achieving temperature signal acquisition. Parallel processing is implemented to prevent temperature acquisition failure by synchronously compensating the subsequent ADC when the preceding ADC samples a new signal. The first temperature drift threshold is a threshold-triggered adaptive temperature drift compensation mechanism. When the detected temperature change exceeds the preset threshold, a dynamic compensation algorithm is activated, outputting the corrected temperature value. A pipelined architecture is used to achieve parallel execution of sampling and compensation. The preceding ADC begins acquiring the next signal while completing the current conversion, overlapping with the compensation processing, thus improving system throughput and reducing overall latency.

[0100] The beneficial effects of this application are:

[0101] This application prevents PWM interference through differential amplification and multi-stage ADC residual error suppression. Furthermore, dynamic temperature drift compensation prevents the cross-effect of temperature on resistors and capacitors, thus mitigating the common problem of lower accuracy with more multiplexed functions. It also achieves progressive optimization of temperature acquisition accuracy through temperature-capacitance linkage compensation.

[0102] In implementation, a complete anti-interference temperature acquisition chain is formed by differential amplification, multi-stage SAR ADC, and temperature compensation, combined with residual error processing to suppress PWM interference. Distributed multiplexing of heating wires and multi-point monitoring enable spatial temperature distribution sensing. Dynamic compensation and parallel processing improve system efficiency and accuracy, enabling high-precision temperature measurement even in steering wheel environments with strong PWM interference.

[0103] Example 5:

[0104] like Figure 4 As shown, the off-hand detection further includes:

[0105] Based on the steering wheel heating wires, the grip characteristics of the steering wheel are obtained, and a mathematical model of the capacitive signal is constructed to determine the real-time gesture characteristics; among which, the grip characteristics include grip area characteristics and grip position characteristics;

[0106] The maximum capacitance value corresponding to the driver's two-hand grip state and the minimum area threshold of the two-hand grip state are determined in advance by peak detection, and a gesture threshold model is constructed.

[0107] The real-time gesture features are input into the gesture threshold model. When the grip area features and grip position features corresponding to the real-time gesture features do not conform to the gesture threshold model, the steering wheel is in the off-hand state.

[0108] In the embodiments of this application, the steering wheel heating wire is used as a gripping carrier. Based on the differences in capacitance distribution of the distributed heating wire, two hand-removal detection features—grip area and grip position—are determined. The reused steering wheel heating wire is used as a sensor to detect the contact characteristics between the driver's hand and the steering wheel. By analyzing the changes in capacitance distribution when the heating wire acts as a capacitance sensor, relevant grip parameters are determined, improving detection accuracy.

[0109] In the embodiments of this application, during the judgment process, the capacitance signal mathematical model converts the distributed capacitance signal of the heating wire into quantifiable grip features, calculates the interaction feature parameters between the current hand and the steering wheel, and determines the grip area and grip position. Combining these two aspects allows for a two-dimensional judgment of the gesture state. The grip area feature characterizes the parameters of the contact area between the hand and the steering wheel. The contact area is calculated based on the size and intensity distribution of the capacitance sensing area, distinguishing different levels of hand weakness. The grip position feature, i.e., the contact position of the hand on the steering wheel, is identified by the capacitance change pattern of the distributed heating wire, thus recognizing the grip posture.

[0110] In the embodiments of this application, the maximum capacitance value is used to characterize the upper limit of the capacitance signal when both hands are normally gripping, which facilitates the detection of valid grip and grip misjudgment under abnormal interference; it is also the peak capacitance value detected when both hands are normally gripping during the calibration stage, so as to achieve personalized adaptation to the driving habits of different drivers.

[0111] In the embodiments of this application, the minimum contact area, the minimum contact area threshold for effective grip, can detect non-hand gripping states and prevent misjudgments caused by partial contact or slight touch.

[0112] In the embodiments of this application, the real-time gesture feature input gesture threshold model achieves dual-dimensional judgment of grip position and grip area during the judgment process, enabling more accurate determination of whether the hand is in a free-hand state. The gesture threshold model judges gesture posture based on multi-dimensional features such as capacitance value, area, and position, and adopts multi-condition logic judgment. Only when multiple feature conditions are met simultaneously can it be determined as a hand-gripping state, reducing the possibility of false judgments.

[0113] In the embodiments of this application, peak detection is used to obtain the maximum capacitance value.

[0114] The beneficial effects of this application are:

[0115] This application utilizes the spatial distribution characteristics of distributed heating wires to determine the differences in capacitance changes among different heating wire segments of the steering wheel, thereby inferring the grip area and grip position. This adapts to the curved surface of the steering wheel and the characteristics of the metal wire electrodes, improving testing accuracy. Grip feature acquisition, modeling, and a threshold model form a complete detection framework; multi-dimensional features and multi-condition judgments work together to achieve accurate state recognition. The spatial information provided by the distributed heating wires, combined with the analytical capabilities of the mathematical model, enhances the system's intelligence. This application, by combining multi-dimensional features such as grip area and position with an intelligent model, can more accurately distinguish between genuine grip and accidental contact, adapting to different grip habits and postures. Although capacitance detection itself is a known technology, using distributed heating wires to extract grip area and position features and constructing a multi-parameter gesture threshold model for intelligent judgment of gesture postures is more accurate.

[0116] Example 6: The heating control circuit includes a switching unit and a pulse width modulation unit, wherein the pulse width modulation unit is electrically connected to the control terminal of the switching unit; wherein,

[0117] The switching unit includes a high-side switch and a low-side switch, which are connected in series in the power supply circuits at both ends of the steering wheel heating wire. The main control unit controls the opening and closing of the high-side switch and the low-side switch to start and stop the heating function.

[0118] The pulse width modulation unit is used to generate a PWM signal with a target duty cycle during the second time period to drive the switching unit to intermittently heat the steering wheel heating wire. The PWM signal with the target duty cycle is determined based on the capacitance change signal so that the capacitance change interference is suppressed within the tolerance of the off-hand detection judgment threshold.

[0119] In the embodiments of this application, the pulse width modulation unit generates a control signal, the switching unit executes power on / off switching, and the switching unit controls the heating wire current, enabling intermittent heating of the steering wheel to suppress interference. The switching unit is a switching component used for controlling the on / off switching of the heating circuit, generally employing semiconductor switching devices such as power MOSFETs or IGBTs to achieve safe on / off control of the heating circuit. The pulse width modulation unit generates a square wave signal with adjustable frequency and duty cycle through a timer or dedicated PWM controller to precisely adjust the heating power. The PWM signal output terminal is connected to the control electrode of the switching device; the PWM signal drives the gate or base of the switching device, controlling its on / off timing.

[0120] In the embodiments of this application, during the control process of the bidirectional switch, the high-side switch and the low-side switch are connected in series at both ends of the steering wheel heating wire, which can achieve complete shutdown of the heating circuit. Shutting down both ends ensures that when heating stops, the heating wire is completely isolated from the power supply circuit, avoiding interference from residual current or voltage to the capacitor detection channel. The high-side switch controls the on / off state of the positive terminal of the power supply, and the low-side switch controls the on / off state of the grounding circuit, forming dual protection. The two switches connected in series in the power supply circuit of the heating wire form a complete safety control link. Through the two-stage switch connection, it is ensured that the heating power is cut off when either stage switch is disconnected.

[0121] In the embodiments of this application, during the process of the main control unit controlling the heating function, it controls the on / off switching of two switches to switch the heating state according to the detection in the first time period and the heating in the second time period, ensuring that heating and detection are completely separated in time and preventing signal superposition interference when working simultaneously. The main control unit independently or collaboratively controls the state of the two switches, outputs control signals through GPIO, and cooperates with the drive circuit to realize the logic control of the power switch, thereby achieving precise start and stop control of the heating function. Then, in the second time period, i.e., a specific time period (such as the heating cycle), a modulation signal with a preset duty cycle is generated to dynamically adjust the conduction time ratio of the PWM signal, thereby achieving time-domain optimized control of the heating power.

[0122] In the embodiments of this application, intermittent heating is used to reduce interference. The PWM signal controls the heating power by adjusting the duty cycle, while avoiding capacitor baseline drift caused by continuous heating. Intermittent heating can reduce temperature fluctuation amplitude, thereby reducing capacitor interference. The intermittent heating mode of the heating wire is achieved through PWM control. Utilizing the switching characteristics of the PWM signal, the heating wire is controlled to switch on and off on a microsecond or millisecond timescale, which can reduce the average heating power and reduce interference from capacitor detection. In the correlation model established between capacitor signal changes and the PWM duty cycle, the set value of the PWM duty cycle is based on the capacitor sensor, i.e., the feedback signal of the correlation model.

[0123] In the embodiments of this application, the PWM duty cycle is adjusted in real time by feeding back the capacitance change signal of the capacitance detection channel, which can adapt to interference changes under different operating conditions. This controls the capacitance interference caused by heating within the allowable error range of the hand-off detection threshold. This ensures that the capacitance detection signal can still accurately display the hand-off / hand-holding state during heating. Duty cycle optimization controls heating interference within an acceptable range for the detection system. Setting an upper limit for the duty cycle ensures reliable detection, fundamentally resolving the functional conflict between heating and detection.

[0124] The beneficial effects of this application are:

[0125] This application achieves electrical isolation of the heating circuit through dual high-side and low-side switches, converting power control via switching into interference isolation. The PWM duty cycle is adjusted using capacitance change signals as feedback. Furthermore, off-hand detection is coupled with heating control to form a cross-functional closed-loop control. The dual-switch safety architecture and intelligent PWM control ensure the safety of the heating system while suppressing electromagnetic interference through adaptive duty cycle adjustment. The redundant design of the high-side and low-side switches provides hardware-level safety, while the capacitor-feedback-based PWM adjustment achieves software-level interference suppression. The dual-switch safety design and capacitor-feedback-based intelligent PWM adjustment significantly improve the system's safety and reliability. In particular, linking duty cycle adjustment to the off-hand detection threshold tolerance addresses the persistent problem of electromagnetic interference in heating environments.

[0126] Example 7:

[0127] The main control unit is connected to a power management circuit, which includes an SBC chip and multiple output branches; wherein, the SBC chip is connected to a successive approximation ADC module, an FIR digital filter and a CAN protocol controller.

[0128] Successive approximation ADC modules are used to acquire differential voltage signals from multiple output branches;

[0129] FIR digital filters are used to convert differential voltage signals into continuous time series current dynamic curves to form a third-order polynomial fitting with real-time temperature as a correction coefficient, and to determine whether there is a power supply abnormality in the output branch.

[0130] Furthermore, when a power supply abnormality occurs, the current dynamic curve corresponding to the output branch with the abnormal power supply is compared with the power supply template, and an abnormal message indicating the power supply deviation can be generated simultaneously through the CAN protocol controller.

[0131] In the embodiments of this application, the SBC chip integrates power management, communication interface, and other functions, making it a high-reliability choice for automotive electronics. Multiple output branches correspond to different circuits requiring power supply. For example, temperature acquisition circuits, heating control circuits, and capacitor detection channels enable synchronous power supply management across multiple output branches. The SBC chip integrates various power management functions, such as current and voltage control, and multiple output branches provide independent power to different modules of the system.

[0132] In the embodiments of this application, the successive approximation ADC is a high-precision voltage signal acquisition method that achieves a good balance between accuracy, speed, and power consumption, making it suitable for multi-channel data acquisition; the FIR digital filter is used to filter out power supply noise and belongs to the finite impulse response digital filter category. It achieves signal filtering of a specific frequency band by performing a weighted moving average on the input signal, and can suppress noise and interference through linear phase response; the CAN protocol controller is a standard vehicle communication interface used for reporting abnormal messages and providing vehicle network communication.

[0133] In the embodiments of this application, differential voltage acquisition is used to suppress common-mode interference and eliminate common-mode noise, so that differential voltage signals can be acquired with high accuracy even in strong interference environments where the vehicle's engine or motor is running, i.e., in harsh electromagnetic environments.

[0134] In the embodiments of this application, the voltage signal is converted into a discrete value by an ADC, and the FIR filter converts it into a continuous current dynamic curve through convolution operation to reflect the transient changes in the current. This prevents misjudgment due to transient noise.

[0135] In the embodiments of this application, third-order polynomial fitting identifies abnormal currents by analyzing the trend of the current dynamic curve, using slope and curvature. The third-order polynomial can describe nonlinear characteristics, and real-time temperature is used as a correction coefficient to improve model accuracy and adapt to the influence of temperature changes on electrical parameters.

[0136] In the embodiments of this application, during real-time temperature correction, to prevent temperature from affecting the resistance value of electronic components, compensation is performed when abnormal currents are identified through third-order polynomial fitting. By pre-storing the current curve characteristics under normal operating conditions using a power supply template, and comparing abnormal curves, specific abnormal types such as overvoltage, undervoltage, and overcurrent are distinguished, thus achieving fault location. The comparison between abnormal curves and templates involves matching the abnormal current curves with a preset fault template library, and using pattern recognition technology to identify specific fault types.

[0137] In the embodiments of this application, the CAN protocol is a standard communication method for in-vehicle networks. Messages indicating power supply deviations can be received by the vehicle controller, triggering protection measures. The CAN protocol encapsulates fault data, including fault type, location, and severity.

[0138] The beneficial effects of this application are:

[0139] This application uses real-time temperature as a correction coefficient for power supply anomaly detection. It employs a third-order polynomial to fit dynamic curve trends and assesses the presence of anomalies based on static thresholds, dynamic trends, and temperature compensation, achieving high-precision power supply anomaly detection. A SAR ADC and FIR filter, in conjunction with current curves and polynomial fitting, perform high-precision signal acquisition and processing. Temperature correction and anomaly detection enhance the environmental adaptability of fault detection. Template comparison and CAN messages form a complete processing chain from fault detection to system notification. Compared to the simple voltage monitoring solutions in traditional vehicles, this approach improves the reliability and maintainability of the power management system through multi-dimensional signal analysis, intelligent temperature compensation algorithms, and standardized fault communication.

[0140] Example 8:

[0141] The input terminal of the power management circuit is connected to a reverse connection protection circuit. The reverse connection protection circuit is constructed using a PMOS transistor and connected in series in the positive power input path to prevent damage to subsequent circuits caused by reversing the positive and negative terminals of the power supply.

[0142] In the embodiments of this application, the input terminal of the reverse connection protection circuit is directly connected to an external power supply. Reversing the polarity will cause the chips of subsequent modules such as the capacitor detection circuit and the heating control circuit to be damaged by reverse voltage, thus preventing damage to the subsequent circuits. Utilizing the conduction characteristics of a PMOS transistor, the PMOS conducts when the power supply is positively connected and is cut off when the power supply is reversed, blocking reverse current. Compared to the diode solutions used by traditional automakers, PMOS has a lower on-state voltage drop, reducing power loss. The PMOS transistor is directly connected in series in the positive power input line. The source of the MOS is connected to the positive power input, the drain is connected to the subsequent circuit, and the gate is controlled by appropriate bias to maintain its conduction state, exhibiting unidirectional conductivity with forward conduction and reverse cutoff.

[0143] In the embodiments of this application, the reverse connection protection circuit needs to be connected in series between the positive terminal of the power supply and the subsequent circuit to cut off the current path when reverse connection occurs. If it is connected in parallel or series in the negative path, it cannot effectively block the reverse current. In the case of reverse power connection, the PMOS transistor is in the cutoff state, cutting off the power supply circuit and realizing circuit protection.

[0144] The beneficial effects of this application are:

[0145] PMOS transistors can be used with gate drive circuits to achieve overcurrent protection and, in conjunction with power management circuits, to protect downstream circuits. The PMOS transistor is connected in series with the positive terminal, and the combination of the two provides efficient, low-loss reverse connection protection. The low on-resistance of the PMOS transistor, combined with its series connection with the positive terminal, provides reverse connection protection while minimizing voltage drop and power loss during normal operation. Using PMOS transistors results in a significantly lower on-state voltage drop, typically tens of millivolts compared to 0.3–0.7 volts for diodes, reducing power loss and heat generation, making them particularly suitable for automotive electronics applications with high efficiency and heat dissipation requirements.

[0146] Example 9:

[0147] The capacitive sensor includes a three-plate differential probe structure, an interface circuit, and a high-voltage excitation phase-sensitive demodulation module.

[0148] The interface circuit includes a charge amplifier, which is electrically connected to the steering wheel heating wire;

[0149] The three-plate differential probe structure includes an upper plate, a lower plate, and an interface electrode. The interface electrode is electrically connected to the interface circuit and determines the capacitance change signal through the upper and lower plates. The upper and lower plates are fixed transmitting electrodes, and a movable mass plate is set between the upper and lower plates.

[0150] The output terminal of the triode differential probe structure is electrically connected to the high-voltage excitation phase-sensitive demodulation module;

[0151] The high-voltage excitation phase-sensitive demodulation module converts the capacitance change signal into a driving voltage signal that adjusts the judgment threshold for off-hand detection through sinusoidal high-voltage excitation and phase-sensitive demodulation; the output of the high-voltage excitation phase-sensitive demodulation module is connected to a multi-stage SAR ADC.

[0152] In the embodiments of this application, a triode differential probe provides a highly sensitive capacitance change signal; an interface circuit amplifies the weak signal and suppresses noise; a high-voltage excited phase-sensitive demodulation module converts the capacitance signal into a driving voltage that can be used for threshold adjustment to achieve the acquisition of the capacitance change signal. The triode structure provides differential detection capability, the interface circuit performs signal conditioning, and the high-voltage excited phase-sensitive demodulation module achieves high signal-to-noise ratio signal extraction.

[0153] In the embodiments of this application, the interface circuit uses a charge amplifier as the core of the interface circuit, which is directly connected to the charge amplifier of the steering wheel heating wire: converting the weak capacitance change signal of the steering wheel heating wire into a mV-level voltage signal to prevent the weak signal from being easily interfered with in the capacitance detection.

[0154] In the embodiments of this application, the triode differential probe structure forms a differential capacitor structure through the upper and lower plates (fixed transmitting electrodes). The upper and lower plates suppress common-mode interference. Specifically, an excitation signal is applied to the upper and lower plates, and the movable mass block plate acts as the sensing electrode to form a differential capacitor structure. Differential measurement suppresses common-mode interference. The interface electrode transmits the differential capacitor signal to the interface circuit, which is the only path for signal output. The output of the triode structure is directly connected to the high-voltage excitation phase-sensitive demodulation module to ensure the shortest signal transmission path and reduce the chance of introducing noise.

[0155] In the embodiments of this application, the movable mass block electrode plate undergoes slight deformation due to pressure / displacement when the driver holds it, resulting in differential changes between the upper and lower electrode plates, which is used to detect weak gripping actions.

[0156] In the embodiments of this application, the differential capacitor signal needs to be modulated by high voltage excitation, and then the fundamental frequency signal related to the gripping action is extracted by phase-sensitive demodulation. If it is directly transmitted to the ADC, the signal will be submerged in noise, causing detection failure. High voltage excitation enhances the signal strength, and phase-sensitive demodulation extracts the component in phase with the excitation signal through synchronous detection, effectively suppressing noise.

[0157] In the embodiments of this application, sinusoidal high-voltage excitation increases the signal amplitude to ensure that weak capacitance changes can be demodulated; phase-sensitive demodulation locks the excitation signal frequency to filter out interference signals such as 50Hz / 1kHz in the vehicle environment; it is converted into a driving voltage signal: the demodulated signal is directly used to adjust the off-hand detection threshold to achieve dynamic linkage between the detection signal and the threshold parameter.

[0158] In the embodiments of this application, the multi-stage SAR ADC improves the conversion accuracy of the driving voltage signal through time-division sampling and error calibration, which facilitates off-hand detection.

[0159] The beneficial effects of this application are:

[0160] This application improves detection sensitivity by using a three-plate differential structure without increasing the number of electrodes. A movable mass is used to suppress interference and amplify the signal, thus enhancing detection sensitivity. Then, high-voltage excitation is used to increase the amplitude, phase-sensitive demodulation filters out interference, multi-stage ADC performs high-precision conversion, and dynamic threshold adjustment is applied. Suppressed noise is filtered out to achieve high-precision hands-off and hands-on detection. The three-plate differential structure and high-voltage phase-sensitive demodulation technology enable the detection of even weaker capacitance changes, resulting in higher sensitivity and anti-interference capabilities. This makes it particularly suitable for applications with extremely high reliability requirements, such as hands-off detection.

[0161] Example 10: As Figure 5 As shown, the capacitor drift further includes the following adjustment steps:

[0162] The capacitance change signal is determined by the temperature acquisition circuit;

[0163] The capacitance change signal is filtered by the SBC chip to generate a capacitance dynamic curve. The capacitance drift is calculated by comparing the real-time capacitance dynamic curve with the preset target capacitance curve.

[0164] Based on the capacitance drift, a PWM signal with a compensating duty cycle is generated. When the capacitance drift is positive, the PWM signal duty cycle is reduced, and when the capacitance drift is negative, the PWM signal duty cycle is increased, so that the real-time capacitance is stabilized within the target capacitance threshold range.

[0165] In the embodiments of this application, temperature is the primary source of capacitance drift. The temperature acquisition circuit provides real-time temperature data to distinguish between capacitance changes caused by genuine gripping and spurious changes caused by temperature drift. Temperature acquisition helps pinpoint the causes of drift. Specifically, capacitance values ​​are affected by temperature; temperature changes lead to changes in the dielectric constant and geometric dimensions, thereby causing capacitance drift. The temperature acquisition circuit provides a reference for temperature compensation.

[0166] In the embodiments of this application, the drift trend is extracted by filtering out high-frequency noise using the FIR filter integrated in the SBC chip, thereby reducing the signal-to-noise ratio of the capacitor signal. Then, a dynamic curve characterizing the drift curve is generated, converting the discrete capacitor signal into a continuous time series that reflects the slow drift trend of the capacitor.

[0167] In the embodiments of this application, the preset target capacitance curve is the capacitance-time relationship under an ideal, drift-free state. The drift amount is accurately calculated by the deviation between the real-time curve and the target curve. The calculation of capacitance drift involves comparing the real-time measured capacitance curve with the pre-stored ideal capacitance curve to quantify the deviation value. The area difference or peak difference between the two curves is calculated using curve matching or difference integration algorithms to obtain the drift amount, thus accurately quantifying the drift.

[0168] In the embodiments of this application, the duty cycle of the PWM signal directly affects the heating power of the steering wheel heating wire, and the drift can be counteracted by adjusting the duty cycle. Specifically, by establishing a mapping relationship between the drift amount and the PWM duty cycle, a compensation signal is output by a controller (such as a PID algorithm).

[0169] In the embodiments of this application, positive drift reduces the duty cycle, heating power, temperature, and capacitance, achieving negative feedback; negative drift increases the duty cycle, heating power, temperature, and capacitance, forming a complete closed loop. Finally, controlling the capacitance drift within the tolerance of the hand-off detection threshold means continuously adjusting the PWM parameters to bring the system operating point to the target range, ensuring that the drifted capacitance signal can still accurately reflect the hand-off / hand-holding state. For positive drift (high capacitance value), the PWM on-time ratio is reduced. Positive drift usually indicates oversensitivity; reducing the duty cycle reduces system gain or heating interference. For negative drift (low capacitance value), the PWM on-time ratio is increased. Negative drift indicates insufficient sensitivity; increasing the duty cycle can enhance the signal or compensate for sensitivity loss.

[0170] The beneficial effects of this application are:

[0171] This application integrates temperature acquisition, curve comparison, and duty cycle adjustment within a millisecond-level closed loop using an SBC chip, converting the temperature signal into PWM compensation commands to achieve integrated control of heating, detection, and compensation. Signal acquisition, drift calculation, and bidirectional PWM compensation constitute an adaptive control loop. Temperature acquisition provides an environmental reference, SBC filtering ensures signal quality, curve comparison accurately quantifies drift, and bidirectional PWM adjustment achieves precise compensation. Ultimately, by ensuring the real-time capacitance remains stable within the target capacitance threshold range, the system maintains detection performance under varying environments. More refined and adaptive drift compensation is achieved through bidirectional PWM duty cycle adjustment (treating positive and negative drifts differently) and dynamic curve comparison.

[0172] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A device for realizing hand-off detection based on a capacitive single-electrode steering wheel, characterized in that, The method comprises the following steps: A master control unit, a capacitive sensor, and a heating control circuit; wherein, The heating control circuit comprises a steering wheel heating wire, the steering wheel heating wire is multiplexed as a sensing electrode of the capacitive sensor, the master control unit is electrically connected with the heating control circuit, and the master control unit controls the current of the steering wheel heating wire; The master control unit is electrically connected with the capacitive sensor, and receives a capacitance change signal of the sensing electrode of the capacitive sensor; At a first time point when the hand-off detection is started, whether there is a capacitance drift is determined according to the capacitance change signal, and a judgment threshold of the hand-off detection is adjusted, and the heating control circuit is turned off; At a second time point when the hand-off detection is turned off and there is a heating instruction, whether a real-time temperature reaches a preset temperature threshold is determined according to the capacitance change signal, and the heating control circuit is turned on to perform heating, and the hand-off detection is turned off; The master control unit is also connected with a temperature acquisition circuit, and the temperature acquisition circuit is used to acquire an ambient temperature in real time; wherein, The temperature acquisition circuit comprises a differential amplification circuit, a multi-stage SAR ADC, and a temperature compensation unit, an input end of the differential amplification circuit is electrically connected with the steering wheel heating wire, the steering wheel heating wire is distributed in a steering wheel holding area; a residual error sampling circuit and a residual error amplification circuit are arranged between each stage of the multi-stage SAR ADC, and are used to suppress the interference of a PWM signal of the steering wheel heating wire; The steering wheel heating wire is used to acquire an ambient temperature analog signal of a plurality of monitoring points on the steering wheel; The differential amplification circuit is electrically connected with an output end of the steering wheel heating wire, and after the ambient temperature analog signal is subjected to noise suppression, the ambient temperature analog signal is input into the multi-stage SAR ADC to generate an ambient temperature digital signal; The temperature compensation unit is electrically connected with a digital signal output end of the multi-stage SAR ADC, and performs dynamic temperature drift compensation on the ambient temperature digital signal through a preset first temperature drift threshold, and outputs a real-time temperature according to the dynamic temperature drift compensation; wherein, when the dynamic temperature drift compensation is performed, a front-stage SAR ADC of the multi-stage SAR ADC synchronously acquires a next temperature analog signal, and parallel processing of sampling and compensation is realized.

2. A device for implementing steering wheel hand-off detection based on a capacitive single electrode direction, according to claim 1, characterized in that, The capacitive sensor is a capacitive digital converter, and the capacitive digital converter comprises at least one touch detection channel and one reference channel; The touch detection channel is electrically connected with the steering wheel heating wire, and the reference channel is electrically connected with a built-in fixed reference capacitor; wherein, the master control unit is used to monitor the capacitance value change of the reference channel to determine a capacitance drift value; And the hand-off detection judgment threshold of the touch detection channel is adjusted based on the capacitance drift value.

3. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 1, characterized in that, The hand-off detection comprises: comparing a real-time sampling value of the touch detection channel with the adjusted hand-off detection judgment threshold, and if the real-time sampling value continuously exceeds the hand-off detection judgment threshold and reaches a preset debounce time, it is determined that a hand is on the steering wheel.

4. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 1, characterized in that, The hand-off detection further comprises: According to the steering wheel heating wire, a holding feature of the steering wheel is acquired, a capacitive signal mathematical model is constructed, and a real-time hand gesture feature is determined; wherein, the holding feature comprises a holding area feature and a holding position feature; A maximum capacitance value corresponding to a double-hand holding state of the driver and a minimum area threshold of the double-hand holding state are determined in advance through peak value detection to construct a hand gesture threshold model. The real-time gesture feature is input into a gesture threshold model, and when the holding area feature and the holding position feature corresponding to the real-time gesture feature do not conform to the gesture threshold model, the steering wheel is in a hand-off state.

5. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 1, characterized in that, The heating control circuit comprises a switching unit and a pulse width modulation unit, and the pulse width modulation unit is electrically connected to the control end of the switching unit. The switching unit comprises a high-side switch and a low-side switch, and the high-side switch and the low-side switch are respectively connected in series in the power supply loop at the two ends of the steering wheel heating wire. The main control unit controls the conduction and shutdown of the high-side switch and the low-side switch to start and stop the heating function.

6. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 1, characterized in that, The pulse width modulation unit generates a PWM signal with a target duty ratio in a second time period to drive the switching unit to intermittently heat the steering wheel heating wire. The main control unit is connected to a power management circuit, and the power management circuit comprises an SBC chip and a plurality of output branches. The successive approximation ADC module connected to the SBC chip is used to collect the differential voltage signals of the plurality of output branches. The FIR digital filter is used to convert the differential voltage signals into a continuous time sequence of current dynamic curves to form a third-order polynomial fitting with the real-time temperature as a correction coefficient to determine whether there is a power supply anomaly in the output branch.

7. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 6, characterized in that, When there is a power supply anomaly, the current dynamic curve corresponding to the output branch with the power supply anomaly is compared with the power supply template to generate an abnormal message labeled with a power supply deviation through the CAN protocol controller.

8. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 1, characterized in that, The input end of the power management circuit is connected to an anti-reverse connection circuit. The capacitive sensor comprises a three-electrode plate differential probe structure, an interface circuit and a high-voltage excitation phase-sensitive demodulation module. The interface circuit comprises a charge amplifier, and the charge amplifier is electrically connected to the steering wheel heating wire. The three-electrode plate differential probe structure comprises an upper electrode plate, a lower electrode plate and an interface electrode, the interface electrode is electrically connected to the interface circuit, and the capacitive change signal is determined through the upper electrode plate and the lower electrode plate. The output end of the three-electrode plate differential probe structure is electrically connected to the high-voltage excitation phase-sensitive demodulation module.

9. A device for detecting the release of a steering wheel based on a capacitive single electrode, as claimed in claim 6, characterized in that, The high-voltage excitation phase-sensitive demodulation module converts the capacitive change signal into a driving voltage signal for adjusting the judgment threshold of the hand-off detection through sinusoidal high-voltage excitation and phase-sensitive demodulation. The capacitive drift further comprises the following adjustment steps: The temperature acquisition circuit is used to determine the capacitive change signal. The SBC chip is used to filter the capacitive change signal to generate a capacitive dynamic curve, and the capacitive drift is calculated by comparing the real-time capacitive dynamic curve with a preset target capacitive curve. According to the capacitance drift amount, a PWM signal with a compensation duty ratio is generated, when the capacitance drift amount is positive, the PWM signal duty ratio is reduced, when the capacitance drift amount is negative, the PWM signal duty ratio is increased, so that the real-time capacitance is stabilized in the target capacitance threshold range.

Images