Method for detecting an impending wheel loss on a vehicle by means of a tire pressure monitoring unit mounted on the wheel

Abstract

A method is described for detecting an impending wheel loss on a vehicle by means of a tire pressure monitoring device (3) mounted on the wheel, which contains a pressure sensor, an acceleration sensor, a transmitter for wirelessly transmitting pressure data and a control unit, wherein vibration data are measured with the acceleration sensor, the vibration data are evaluated and, upon detection of an anomaly in the vibration data, a warning signal is generated to indicate an impending wheel loss.

Description

[0001] The invention relates to a method for detecting an impending wheel loss on a vehicle using a tire pressure monitoring unit mounted on the wheel. A method having the features specified in the preamble of claim 1 is known from US 2008 / 0 243 327 A1. Similar methods are known from DE 10 2018 128 453 A1, DE 103 16 705 A1, and US 2014 / 0 309 860 A1.

[0002] Tire pressure monitoring units are mounted on vehicle wheels, typically on a tire valve or on the rim. Such tire pressure monitoring units are known, for example, from DE 10 2020 120 052 A1 and contain a pressure sensor, an acceleration sensor, and a transmitter for wirelessly transmitting pressure data to a receiving unit in the vehicle.

[0003] In vehicles equipped with tire pressure monitoring units, excessive or underinflated tire pressure can be indicated to the driver, for example, by a warning light on the dashboard. However, tire pressure monitoring units are also increasingly being integrated into vehicle safety systems. This means that the data they report is evaluated by a central unit in the vehicle, which intervenes in critical situations, for example, to keep the vehicle in lane and brake in the event of a tire burst.

[0004] The object of the present invention is to show a way in which vehicle safety can be further improved with tire pressure monitoring units.

[0005] This object is achieved by a method having the features specified in claim 1. Advantageous developments of the invention are the subject of subclaims.

[0006] In a method according to the invention, vibration data is measured using an acceleration sensor of a tire pressure monitoring device mounted on a wheel. The vibration data is then evaluated, and if an abnormality is detected in the vibration data, a warning signal is generated to indicate impending wheel loss. This warning signal can then be processed, for example, by a vehicle safety system and / or activate a warning light on the dashboard.

[0007] The vibration data can be evaluated in the tire pressure monitoring unit or in a central unit in the vehicle that communicates wirelessly with the vehicle's tire pressure monitoring units. Preferably, the evaluation is performed by a control unit of the tire pressure monitoring unit. This advantageously reduces the volume of data to be transmitted, as no vibration data needs to be transmitted, only a warning signal in case of imminent wheel loss.

[0008] According to the invention, when evaluating the vibration data, a signal value is compared with a predetermined threshold value. If the threshold value is exceeded, an imminent wheel loss is determined. If a wheel detaches from an axle, increased vibrations occur at that wheel. Imminent wheel loss can therefore be detected by comparing vibration data with a threshold value. For example, to evaluate the vibration data, the root mean square of a predetermined number of measured values ​​from an acceleration sensor of the tire pressure monitoring unit can be calculated and compared with a threshold value, for example, from the last 10 to 50 values.

[0009] A further advantageous development of the invention provides that the threshold value is dynamically specified depending on previously measured vibration data. The extent of the vibrations occurring at a wheel naturally also depends on the road surface and the vehicle speed. The rotational frequency of the wheel and thus the vehicle speed can be determined from data from an acceleration sensor. Since the vehicle speed typically only changes over periods of approximately one minute during conventional acceleration processes, the threshold value is preferably determined taking into account vibration data from the past 30 to 60 seconds. In this way, the effects of the road surface on the vibrations can also be taken into account.

[0010] When a wheel is about to become loose, not only do vibrations increase, but the vibration data measured are less periodic and characterized by increased noise. A further advantageous development of the invention therefore provides that a Fourier transformation of vibration data is performed during the evaluation and the threshold value for a frequency is specified. The frequency spectrum of the vibration data generally has a maximum at the rotational frequency of the wheel. When a wheel is about to become loose, increased contributions also occur at other frequencies, so that the risk of wheel loss can be more clearly identified by performing a Fourier transformation and then specifying the threshold value for a frequency in the spectrum. This frequency is preferably higher than the rotational frequency of the wheel.

[0011] According to the invention, the tire pressure monitoring unit monitors an electrical capacitance between a metal part of the tire pressure monitoring unit and a rim of the wheel, and calculates the threshold value as a function of these measurement signals. The rim of a vehicle wheel, together with the axle, forms a kind of antenna that is capacitively coupled to a metal part of the tire pressure monitoring unit, for example, a metallized surface of a circuit board. If a vehicle wheel becomes loose and moves relative to the axle, this antenna configuration changes, i.e., the capacitance measurable at the metal part changes. A change in capacitance in combination with increased vibration therefore indicates particularly reliably the risk of wheel loss.

[0012] To monitor capacitance, it is not necessary to measure the capacitance directly or to determine absolute values. Since a change in capacitance occurs when a wheel is about to fail, it is sufficient to determine measurement signals that correlate with the capacitance. Such measurement signals can be, for example, the resonant frequency of an oscillating circuit containing the capacitance or deviations of the resonant frequency from a specified excitation frequency of the oscillating circuit.

[0013] An advantageous development of the invention provides that an alternating voltage is generated by the tire pressure monitoring unit to measure the capacitance and applied to the metal part. The capacitance can then be measured, for example, by measuring the resonant frequency of an oscillating circuit containing this capacitance. This resonant frequency is typically between 500 Hz and 10 MHz. An alternating voltage for measuring the capacitance can be generated, for example, by chopping a battery voltage or using a PLL (phase-locked loop). Changes in the resonant frequency, and thus in the capacitance, can be measured, for example, using a voltage divider circuit.

[0014] The metal part can, for example, be a metallized surface of a circuit board of the tire pressure monitoring device.

[0015] The threshold value against which the vibration data is compared when evaluating it can then be adjusted as a function of the capacity, for example by means of a characteristic curve or a characteristic map.

[0016] Further details and advantages of the invention are explained using an exemplary embodiment with reference to the accompanying drawings. They show: Fig. 1 an embodiment of a tire pressure monitoring unit with a valve and a rim; Fig. 2 an exploded view of the tire pressure monitoring unit, and Fig. 3 a circuit diagram for monitoring the capacitance formed by a metal part of the tire pressure monitoring device and a rim.

[0017] In Fig. 1 shows a rim 1 in a sectional view together with a tire valve 2 and a tire pressure monitoring unit 3 mounted thereon. This tire pressure monitoring unit is in Fig. 2 shown in an exploded view.

[0018] The tire pressure monitoring unit 3 has a housing 32 closed by a cover 31, in which a voltage source 34, for example a battery, a circuit board 33 with a pressure sensor, a temperature sensor, an acceleration sensor, a transmitter unit, and a control unit are arranged. The transmitter unit for wirelessly transmitting pressure data and other information is provided with an antenna 35, for example in the form of a bracket.

[0019] During operation, the acceleration sensor measures vibration data, which is then evaluated by the control unit of the tire pressure monitoring unit 3 or a central receiving unit of the vehicle. If an abnormality is detected in the vibration data, a warning signal is generated to indicate impending wheel loss. This signal can, for example, be provided to a vehicle safety system and / or activate a warning light on the vehicle's dashboard.

[0020] For example, when evaluating vibration data, a signal value can be compared to a predefined threshold, and if the threshold is exceeded, an imminent wheel loss can be determined. For example, to evaluate vibration data, the root mean square of a predefined number of measured values ​​from an acceleration sensor of the tire pressure monitoring unit can be calculated and compared to a threshold, for example, from the last 10 to 50 values.

[0021] The threshold can be dynamically set based on previously measured vibration data. For example, a vibration increase of more than double over a specified period of time, such as 30 to 60 seconds, can be used as an indication of the risk of wheel loss.

[0022] An improvement can be achieved by performing a Fourier transformation of vibration data during evaluation and specifying a threshold value for a specific frequency. The frequency spectrum of the vibration data typically peaks at the wheel's rotational frequency. When a wheel is coming loose, increased contributions also occur at other frequencies, so the risk of wheel loss can be more clearly identified by performing a Fourier transformation and then specifying a threshold value for a frequency in the spectrum that is higher than the wheel's rotational frequency.

[0023] An improvement can also be achieved by setting the threshold value as a function of a measured capacitance measured between a metal part of the tire pressure monitoring unit 3, such as a metallized surface 36 of the circuit board 33, and a rim of the wheel.

[0024] The rim 1 of a vehicle wheel, together with the axle, forms a kind of antenna that is capacitively coupled to a metal part of the tire pressure monitoring unit, for example, a metallized surface of a circuit board. When a vehicle wheel becomes loose and moves relative to the axle, this antenna configuration changes, i.e., the capacitance measurable at the metal part changes. A change in capacitance combined with increased vibration therefore reliably indicates the risk of wheel loss.

[0025] During operation, the control unit of the tire pressure monitoring unit measures this capacitance at regular intervals. For example, by applying an alternating voltage to the metallized surface 36, approximately in the range of 500 Hz to 10 MHz, in particular in the range of 1 MHz to 10 MHz. This alternating voltage can be generated, for example, by chopping a voltage supplied by the voltage source 34, i.e., by chopping a battery voltage.

[0026] As soon as a wheel begins to detach from the axle, the capacitance formed between the metallized surface 36 and the wheel rim 1 changes. By measuring and evaluating the capacitance formed between the metallized surface 36 and the wheel rim 1, the risk of wheel loss can be identified. For example, the control unit can compare the measured capacitance with a standard range, and if a capacitance outside the standard range is detected, the threshold value against which a signal value of the vibration data is compared can be reduced, for example, using a characteristic curve.

[0027] The standard range for capacity can be defined, for example, from historical measurement data, especially from measurements of capacity when the vehicle is parked. The standard range can thus be redefined for each trip. For example, the standard range can be defined such that a deviation from a standard value when the vehicle is parked by more than a specified percentage indicates impending tire failure.

[0028] For example, the capacity can be measured at relatively long intervals while the vehicle is parked, such as every hour or more. If the acceleration sensor detects the start of a journey, the time intervals between capacity measurements can be shortened, for example, to 1 second to 1 minute.

[0029] Fig.Figure 3 shows a sketch of a circuit for measuring capacitance C, which is formed by a metal part of the tire pressure monitoring device, such as the metallized surface 36 of the circuit board 33, and the rim 1. The rim 1, together with a vehicle axle connected to it, forms a kind of antenna. The capacitance C can therefore be regarded as part of an oscillating circuit or an antenna circuit. This antenna circuit is fed by a high-frequency generator 4 via a resistor R1, i.e., an alternating voltage is applied to the capacitance. For this purpose, the high-frequency generator 4 is connected in series with the resistor R1 and the capacitance C. The capacitance C is therefore conductively connected to a point between the two resistors R1, R2.

[0030] Resistor R1, together with resistor R2, forms a voltage divider. The voltage applied between the two resistors R1 and R2 depends on how much energy is radiated by the antenna, i.e., in particular, on how close the excitation frequency of the high-frequency generator 4 is to the resonant frequency of the oscillating circuit. If capacitance C changes, the voltage between resistors R1 and R2 also changes. Capacitance C can therefore be monitored by measuring the voltage between the two resistors R1 and R2 with a voltmeter, such as an analog-to-digital converter (AD). The voltage between the two resistors R1 and R2 is thus a measurement signal that correlates with capacitance C. If this voltage lies outside a specified standard range, it can be concluded that a tire is at risk of failure.

[0031] The two resistors R1 and R2 are the same size in the example shown, but they can also differ. Deviations of up to 20% are generally unproblematic. List of reference symbols 1 rim 2 valve 3 Tire pressure monitoring unit 31 lids 32 housings 33 circuit board 34 Voltage source 35 Antenna 36 metallized surface

Claims

[1] Method for detecting an impending wheel loss on a vehicle by means of a tire pressure monitoring device (3) mounted on the wheel, which contains a pressure sensor, an acceleration sensor, a transmitter for wirelessly transmitting pressure data and a control unit, where vibration data is measured with the acceleration sensor, the vibration data is evaluated, If an abnormality is detected in the vibration data, a warning signal is generated to indicate an impending wheel loss and When evaluating the vibration data, a signal value is compared with a specified threshold value and, if the threshold value is exceeded, an impending wheel loss is concluded, characterized by that an electrical capacitance between a metal part (36) of the tire pressure monitoring unit (3) and a rim (1) of the wheel is monitored by means of the tire pressure monitoring unit (3), and the threshold value is calculated depending on measurement signals correlating with the capacity. [2] Method according to claim 1, characterized by that the threshold value is set dynamically depending on previously measured vibration data. [3] Method according to one of the preceding claims, characterized by that a Fourier transformation of vibration data is carried out during the evaluation and the threshold value for a frequency is specified. [4] Method according to claim 3, characterized by that the frequency is greater than the rotational frequency of the wheel. [5] Method according to one of the preceding claims, characterized bythat the measurement signals correlating with the capacitance are voltage values ​​which are determined by means of a voltage divider formed from a first resistor (R1) and a second resistor (R2), a high-frequency generator (4) which is connected in series with the metal part (36) via the first resistor (R1), and a voltmeter (AD) for measuring a voltage between the first resistor (R1) and the second resistor (R2).

Images