Tire sensor system and method

Abstract

A tire sensor system and method are provided. A tire sensor system mountable in a wheel of a vehicle for determining a desired characteristic of the wheel or its tire or the road, comprising: an autonomous electric energy source, a conductor, a wireless data interface transmitting a signal providing the desired characteristic to the vehicle, characterized by an electronic circuit configured to acquire, filter and digitize a capacitance of the conductor and determine the signal transmitted to the vehicle based on the digitized capacitance.

Description

Technical Field

[0001] This invention relates to a wireless instrument and corresponding method for monitoring vehicle wheels. Background Technology

[0002] Tire pressure monitoring systems (TPMS) have been adopted by many automakers and have indeed been mandatory in most major automotive markets for many years. In many implementations of this concept, each tire is equipped with a disposable TPMS device fixed to the rim, facing the interior air space. The disposable TPMS device includes an autonomous power source (typically a button cell battery) designed to last for many years, pressure sensors, and hybrid miniaturized circuitry configured to acquire, digitize, and process the internal tire pressure, then wirelessly transmit a signal to the vehicle that is suitable for alerting the user when the pressure in any tire drops below a pre-programmed threshold.

[0003] Typically, the TPMS system and inflation valve are integrated together and constitute a single replaceable part. Wireless transmission can occur within specific bands of the radio spectrum, such as 315 MHz or 433 MHz. Recently, Bluetooth Low Energy (BTLE) has been increasingly used to provide a two-way secure link in these applications.

[0004] TPMS systems may include sensors other than pressure sensors. For example, U.S. Patent 10,850,578 discloses a TPMS system with an acceleration sensor and a temperature sensor.

[0005] Capacitive sensors are commonly used in electronic devices as proximity sensors and touch input devices. Among many examples, U.S. Patent 11,082,550 in the name of this applicant provides one. Summary of the Invention

[0006] This invention proposes a sensor system and method that overcomes at least some of the shortcomings and limitations of the prior art.

[0007] According to the present invention, a tire sensor system that can be installed in the wheel of a vehicle for determining desired characteristics of the wheel or its tire or road includes: an autonomous electrical power source, a conductor, and a wireless data interface for transmitting a signal providing the desired characteristics to the vehicle. The system is characterized by electronic circuitry configured to acquire, filter, and digitize the capacitance of the conductor, and to determine the signal transmitted to the vehicle based on the digitized capacitance. The conductor will also be referred to hereinafter as a "sensing electrode".

[0008] The dependent claims relate to important and useful but not essential features. The tire sensor system is intended to be installed in the wheels of automobiles, trucks, motorcycles, or any other on-road or off-road vehicle. The conductor's position is chosen such that capacitance indicates, for example, the instantaneous proximity between the conductor and the road surface, and, depending on the wheel's rotation angle, to nearby surfaces of the vehicle (such as fenders). By analyzing the temporal evolution of the capacitance, the system can infer desired characteristics, which may be, for example, the wheel's rotation angle, its angular velocity, and the direction of rotation. The capacitance value is also affected by tire compression, and therefore by wheel load, and the sensor system can be configured to extract these information elements as well.

[0009] The position of the wheels relative to the vehicle body provides information about the shock absorber position, and this can be used alone or in combination with tire compression to determine road quality (smooth vs. bumpy) and whether the road surface is wet or dry. These values ​​can be used to improve the accuracy of pressure measurements (by correcting for pressure measurements by taking compression into account). Tire load and shock absorber position values ​​can be provided to the ESP system for better vehicle stability control. Thread height also affects the measured capacitance, and this system can be used to determine tire wear. Determination of rotation direction can be a valuable input to parking assist systems.

[0010] The tire sensor system of the present invention can be located on the wheel rim facing the internal air chamber, or on the inner surface of the tire facing the air chamber, or embedded in the tire material. Advantageously, the conductor can be realized as a metallized surface on a flexible or rigid printed circuit; therefore, the sensor system of the present invention can be implemented very economically, it is simple to adapt the geometry of the conductor to the available space in different vehicles, wheels and tires, and the capacitive electrodes themselves are very lightweight, having little or no impact on the balance of the wheel.

[0011] To improve capacitance determination, the conductor is preferably protected by adjacent active barriers driven by electronic circuitry and / or passive barriers grounded.

[0012] The invention also includes corresponding methods for determining desired characteristics of tires, wheels, or roads in a vehicle, as defined by the claims in the corresponding class. Attached Figure Description

[0013] Exemplary embodiments of the present invention are disclosed in the specification and illustrated in the accompanying drawings, wherein: Figure 1 The wheels of a vehicle equipped with the contact monitoring system of the present invention are shown in a simplified manner.

[0014] Figure 2 This is a simplified schematic diagram of the contact monitoring system of the present invention.

[0015] Figure 3This is a simplified example among many possible variations of the circuit used in this invention to convert the self-capacitance of a general electrode into a digital value.

[0016] Figure 4 An example of digital processing that can be used in this invention is illustrated.

[0017] Figure 5 The invention is shown operating in a rolling tire.

[0018] In each figure, noteworthy elements are identified by repeated reference numerals in the text. The same reference numerals can be used to identify different elements that are identical, similar, logically related, or technically equivalent. When many identical, similar, related, or equivalent elements appear in a figure, some reference numerals may be omitted to avoid confusion. Detailed Implementation

[0019] Figure 1 An example of the invention is shown, wherein a sensor system 51 is mounted on the rim 74 of a vehicle wheel, facing the interior air space 99. The sensor includes an autonomous power source 53 (e.g., a button battery), a conductor 55 configured as a capacitive sensing electrode, and circuitry 58 capable of determining the self-capacitance of the sensing electrode and estimating the distance between the electrode and the preceding conductor or high-permeability body. The processing results are then wirelessly transmitted to the vehicle, for example, to the ECU.

[0020] Positioning the sensor system on the wheel rim is the most common approach for TPMS systems and offers several advantages: the sensor can be integrated with the air valve, does not interfere with tire changing and repair, and has minimal impact on wheel balance or driving characteristics. However, this is not the only possible solution. The system, or the very lightweight single electrode 55, can be positioned elsewhere, such as on the inner surface of the sidewall 96, on the ceiling 97 of the interior space 99, or embedded in the material of the tire 92.

[0021] Figure 2 Electronic circuitry 30 is shown. The detector has two inputs, each connectable to a capacitive sensing electrode 55 and an active barrier electrode 54 located below. An optional ground barrier 56 is also provided. It should be understood that the configuration of the electrodes and barriers shown here is purely for illustrative purposes and can vary considerably. The number of sensing electrodes, barriers, and ground planes is not constrained.

[0022] In this example, but this is entirely optional, the circuitry provides additional inputs that can be connected to more capacitive sensing electrodes or barriers or other general-purpose sensors 71 (such as temperature and pressure sensors). The underlying mechanism for converting temperature, force, or pressure into electrical signals can be capacitive, resistive, inductive, or have any other properties.

[0023] Internally, the capacitance detector 30 has an analog-to-digital converter 40 that converts the capacitance signal into a digital signal suitable for further processing in the digital processor 45. Preferably, a common converter is used to sequentially read the capacitance seen by the sensing electrodes via a multiplexer 35. However, this is not an absolute requirement.

[0024] The input unit 31, linked to the capacitive sensing electrode, is configured to set the corresponding input terminal to a desired state selected from measurement state, ground state, high impedance state, and barrier state. In measurement state, the input potential is variable, following a variable voltage source in the capacitive sensor device, and the resulting charge change is sent to the ADC to determine the capacitance value. In ground state, the input remains at a constant voltage, either the ground voltage or a fixed offset. In barrier state, the voltage at the input follows the voltage of another input in measurement state, but charge changes are ignored.

[0025] Input unit 32 will be configured based on the specific requirements of the sensors attached to it. If the sensors 71 are capacitive in nature, they can be the same as unit 31, or they can be different if other principles are used, such as if a thermistor or resistive pressure transducer is present.

[0026] Circuit 30 also includes a logic engine 41, which has general functions for orchestrating the system, sequentially activating the required input units and multiplexers, determining the usage mode of each input (measurement, barrier, ground, high Z, or others), etc.

[0027] Further to the right, circuit 30 connects to host processor 57, which receives capacitance and sensor measurements, processes them further (if necessary), and transmits them to the vehicle via a suitable wireless link. Optionally, the host processor may have optional analog input pins that serve other sensors 73, and their readouts are also transmitted over the wireless channel. Preferably, the wireless channel is bidirectional and allows the sensor system to be reprogrammed or tuned in the field. Depending on the vehicle's requirements, the wireless link may be radio-based and use Bluetooth LE radio or a transmitter at 315 MHz or 433 MHz. The antenna may be a planar antenna etched onto printed circuitry, on which the system is mounted, and in a particularly advantageous combination, the same conductor pad 55 can provide dual service as both a proximity electrode and an antenna, with the two signals sufficiently separated in frequency to avoid interference.

[0028] The configuration shown in this example is not required: the invention may also include variations in which the system comprises more than two integrated circuits, and other variations in which all systems are integrated in a single chip or package.

[0029] Figure 3 A possible implementation of an input unit is shown in a very simplified form, which causes the voltage at the input to follow a variable voltage source and can be used within the framework of this invention to convert capacitance into a digital value using ADC 40. This is provided for the completeness of this disclosure and as an example, but the invention also includes other structures for the input stage that can provide the desired functionality. A sensing electrode is connected to an SC node, which is linked to the inverting input of amplifier 32, while another input is driven by a voltage source 36 that can provide a variable or constant voltage. Due to feedback, the SC node is a low-impedance node, and its voltage is the same as (possibly with a constant offset, which is not significant in this application) the voltage of voltage source 36.

[0030] The grounding state of input node SC can be obtained by generating a constant voltage from source 36. Input node SC is then virtually grounded. When source 36 generates a variable voltage, the measurement state and barrier state are obtained. Node SC then follows this voltage.

[0031] The capacitance of the sensing electrode connected to the SC node can be measured by generating a series of steps at source 36. Capacitor 34 connected in the reaction loop acts as an integrator, and the output of amplifier 32 will show a step proportional to the change in charge on the sensing electrode. By definition, the ratio between the charge measurable as a step voltage at the output of amplifier 32 and a known voltage step at source 36 is the desired capacitance. Switch 33 is used to periodically discharge the reaction capacitor 34. The input unit may also include a switching element (not shown) to disconnect node SC and place it in a high-impedance state.

[0032] The output signal is digitized by ADC converter 40, preferably synchronized with the pulse of source 36. Multiplexer 35, preamplifier 38 and offset correction 39 are not shown in this figure, but may be present.

[0033] For example, Figure 4 This is a schematic diagram of digital processing occurring in digital processor 45. Raw data from the ADC is processed by a first low-pass filter 94, which may include linear and nonlinear filter elements. The resulting variable (USE) is also fed to a baseline determination unit 95, which may also include a linear low-pass filter used for averaging and nonlinear operations, and subtracts the average baseline (AVG) from the filtered signal to generate a differential capacitance (DIFF). Importantly, the average baseline is also fed to a discriminator, and when its value exceeds a set threshold, a signal is fed back to... Figure 3 The analog offset compensation circuit 39. The second comparator provides a logic proximity flag (STAT). The circuit is drawn as if the logic flag (STAT) constitutes the output, but in the actual implementation, all variables (RAW, USE, AVG, DIFF, STAT) can be transferred to the host system or vehicle as needed.

[0034] Figure 5 The illustration depicts the operation of an embodiment of the invention. The upper part of the figure shows a car wheel equipped with the sensor system 51 of the invention on a rim 74, the sensor system 51 facing the internal air space 99 in two orientations. In the first orientation, the rotation angle is conventionally specified. The sensor faces upward and transmits a proximity signal, which is primarily affected by the distance d1 to any conductor located above it (in this case, the mudguard 98).

[0035] The second orientation is opposite to the first orientation and has a rotation angle. Sensor 51 faces downwards and transmits a proximity signal determined by the distance d2 to the road surface below. Since d2 is much shorter than d1—both because the road surface 91 contacts the tire's threaded surface and because of the tire's compression under load—the proximity signal will show a peak whenever the wheel adopts this orientation.

[0036] The lower part of the diagram shows the proximity signal 88 during one full wheel revolution, illustrating... The peak value at that point. The signal shown is the DIFF signal after subtracting the baseline (see...). Figure 4 (), and only the effect of proximity to the road surface 91 is shown.

[0037] As the vehicle is moving, the PROX signal exhibits periodically repeating peaks whenever the sensing pad looks down. The period between peaks is proportional to the angular velocity of the wheel, while the height of the peaks is correlated with distance d2 and is affected by tire compression and tread wear. The system sensors of this invention can then extract these characteristics from the proximity signal 88. Tire compression can be used to determine an indicator of road smoothness or bumpiness and can reveal wet road conditions. All these characteristics are transmitted to the vehicle to improve stability and handling and / or warn the driver.

[0038] Signal 88 only shows the effect of the road surface 91, while the area far away... The curve for the peak at d1 is featureless; however, the measurement system is also affected by vehicle parts, such as the fender at distance d1. In this case, a broader and less distinct peak is expected to be concentrated... Surroundings. These characteristics of signal 88 can be used to extract other desired properties, such as the distance between the rotation axis and fender 98, which is correlated with the extension of the shock absorber. This information can be used in sensor systems to extract indicators of road quality (bumpy or smooth) or its wet / dry condition, which are then transmitted to the vehicle's ECU and / or the driver to improve handling and safety.

[0039] Tire compression can affect pressure readings and is a source of error in conventional TPMS systems. The system of this invention can compensate for this effect and provide more accurate pressure readings under dynamic conditions. The compression difference across the four wheels is also important for vehicle stability and, for this purpose, can be transmitted to the ESP system.

[0040] The sensor system of the present invention can be programmed to detect the difference between the rotational speed of the wheel and the rotational sensing, which may be useful in assisted parking systems.

[0041] The systems and methods disclosed herein can be modified and improved in several ways without departing from the scope of the appended claims. For example, the system may include more than one sensing electrode positioned at different angles on the rim or tire. This additional information can be used to more accurately determine the rotation angle of the wheel and its rotation sensing. Multiple electrodes may be oriented differently to be more sensitive to the proximity of different objects, such as distinguishing between a signal triggered by proximity to the road and another signal triggered by proximity to vehicle parts. For the same effect, the directionality of the capacitive sensor can be variable by arranging programmable barrier electrodes that can switch between an active barrier state and a ground state, or switch to a high Z state.

[0042] Reference symbols in each figure 30 Capacitive Proximity Sensor Circuit 31 C to V converter 32 General-purpose analog front-end 33 Reset Switch 34 Integrating Capacitor 35 Multiplexer 36 Variable Voltage Source 38 Simulation Preprocessing 39 Offset Subtraction 40 ADC 41 Logic Engine 45 Digital Data Processing 51 Tire contact sensor 53. Batteries and Energy 54 Barriers 55 Sensing Pads 56 Grounding plane 57 host 58 Electronic Circuits 71 Sensors 73 Sensors 74 rims 88 Proximity Signal Road 91 92 tires 94 ADC and original low-pass filter 95 average units 96 Inner wall 97. Ceiling 98 Mudguard 99. Internal air space.

Claims

1. A tire sensor system that can be mounted in a vehicle wheel for determining desired characteristics of the wheel or its tire or road, comprising: - Independent electric energy source - Conductor, - A wireless data interface that transmits signals to the vehicle providing the desired characteristics, characterized in that... - Electronic circuitry configured to acquire, filter, and digitize the capacitance of a conductor, and determine the signal transmitted to the vehicle based on the digitized capacitance.

2. The tire sensor system of claim 1, which is mounted in the wheel, wherein the conductor is positioned such that the capacitance indicates the instantaneous proximity between the conductor and the road and / or a vehicle surface adjacent to the wheel, the instantaneous proximity varying with the rotation angle of the wheel.

3. The tire sensor system according to claim 1, wherein the conductor facing the inner air chamber is located on the rim of the wheel, or facing the air chamber is located on the inner surface (96, 97) of the tire, or is embedded in the tire material.

4. The tire sensor system according to claim 1, wherein the conductor is a metallized surface on a flexible or rigid printed circuit.

5. The tire sensor system of claim 1, wherein the conductor is adjacent to an active barrier driven by the electronic circuit, such that the potential of the active barrier follows the potential of the conductor during the acquisition of the capacitor, and / or adjacent to a passive barrier grounded.

6. The tire sensor system according to claim 1, wherein the desired characteristic is one of the following: instantaneous wheel angle, angular velocity of the wheel, rotation direction of the wheel, tire compression, tire load, thread wear, position of shock absorber, road quality, and road humidity.

7. A method for determining desired characteristics of a tire, wheel, or road in a vehicle, comprising: - Provides autonomous power, a conductor, and a wireless data interface for transmitting signals to the vehicle within the wheel, the signals providing the desired characteristics, characterized in that... - Use electronic circuits to collect, filter, and digitize the capacitance of conductors. - The signal transmitted to the vehicle is determined based on the digital capacitance.

8. The method of claim 7, further comprising placing the conductor in the wheel such that its self-capacitance depends on the rotation angle of the wheel by a change in the instantaneous proximity between the conductor and the road and / or a vehicle surface adjacent to the wheel.

9. The method of claim 7, comprising determining one of the following: instantaneous wheel angle of the wheel, angular velocity of the wheel, rotational direction of the wheel, tire compression, tire load, thread wear, position of shock absorber, road quality, and road humidity.

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