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

Abstract

A method is described for detecting an impending wheel loss on a vehicle by means of a tire pressure monitoring unit (3) mounted on the wheel, wherein 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), measuring signals correlating with the capacitance are compared with a standard range, and upon detection of measuring signals outside the standard range, a warning signal is generated to indicate an impending wheel loss.

Description

[0001] The invention relates to a method for detecting impending wheel loss on a vehicle using a tire pressure monitoring unit mounted on the wheel. DE 10 2007 046 492 A1 discloses a method for detecting impending wheel loss, in which an inductance between a metal part of the tire pressure monitoring unit and a wheel rim is monitored. If values ​​outside a normal range are detected, a warning signal is generated to indicate impending wheel loss. Further methods for detecting impending wheel loss are known from DE 103 16 705 A1, DE 10 2018 128 453 A1, and US 2008 / 0 243 327 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 and by a tire pressure monitoring unit according to claim 8. Advantageous developments of the invention are the subject of subclaims.

[0006] In a method according to the invention, an electrical capacitance between a metal part of the tire pressure monitoring unit and a wheel rim is monitored using a tire pressure monitoring unit mounted on a wheel. Measurement signals correlating with the capacitance are then compared with a standard range. If these measurement signals lie outside the standard range, an impending wheel loss is determined, and a warning signal is generated. By detecting impending wheel loss at an early stage, vehicle safety can be significantly improved. The warning signal can, for example, be processed by a vehicle safety system and / or activate a warning light on the dashboard.

[0007] 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.

[0008] The evaluation of measurement signals to determine the capacity, and in particular the comparison with the standard range, can be performed in the tire pressure monitoring unit or in a central unit in the vehicle that communicates wirelessly with the 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.

[0009] 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. When a vehicle wheel detaches and moves relative to the axle, this antenna configuration changes, meaning the capacitance measurable at the metal part changes.

[0010] An advantageous development of the invention provides that, to measure the capacitance, an alternating voltage is generated by the tire pressure monitoring unit 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.

[0011] The measured capacitance or the resonant frequency of an oscillating circuit containing this capacitance is compared with a standard range defined by historical measurements. For example, the standard range can be redefined at the start of each trip, such that a deviation of more than a specified percentage indicates impending tire failure.

[0012] The sensitivity of detecting impending wheel loss can be increased and false positive warning signals avoided by additionally evaluating signals from an acceleration sensor in the tire pressure monitoring unit. When a wheel begins to detach from an axle, increasingly larger movements of the wheel relative to the axle occur. This leads to increasing vibrations of the wheel and thus to corresponding acceleration signals. To detect this, the root mean square can be calculated from a given number of measured values ​​from an acceleration sensor in the tire pressure monitoring unit, for example, and the normal range can be defined based on this, for example as a map. For example, the root mean square can be calculated from the last 10 to 50 values.

[0013] 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.

[0014] 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.

[0015] 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.

[0016] The circuit board 33 has a metallized surface 36, which, together with the rim 1, forms a capacitance. During operation, the control 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, particularly 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.

[0017] When driving, there is always the possibility that a wheel will become detached from the axle of a vehicle. As soon as a wheel begins to detach from the axle, the capacitance formed by the metallized surface 36 with the rim 1 of the wheel changes. By measuring and evaluating the capacitance formed by the metallized surface 36 with the rim 1 of the wheel, the risk of a wheel becoming detached can be identified. To do so, the control unit compares the measured capacitance with a standard range and, if a capacitance outside the standard range is detected, generates a warning signal to indicate an impending wheel becoming detached. This warning signal can be made available to a vehicle safety system and / or activate a warning light on the vehicle's dashboard.

[0018] 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.

[0019] 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.

[0020] The sensitivity of detecting impending wheel loss can be increased and false positive warning signals avoided by additionally evaluating signals from an acceleration sensor in the tire pressure monitoring unit. When a wheel begins to detach from an axle, increasingly larger movements of the wheel relative to the axle occur. This leads to increasing vibrations of the wheel and thus to corresponding acceleration signals. To detect this, the root mean square can be calculated from a given number of measured values ​​from an acceleration sensor in the tire pressure monitoring unit, for example, and the normal range can be defined based on this, for example as a map. For example, the root mean square can be calculated from the last 10 to 50 values.

[0021] For example, if a standard capacitance range is defined from historical measurement data, such as measurements of capacitance while the vehicle is parked, the maximum permissible deviation from a standard capacitance value can be reduced the more the vibrations measured by the acceleration sensor are. The permissible standard range can thus be defined as a characteristic map.

[0022] 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.

[0023] 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.

[0024] 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 unit (3) mounted on the wheel, wherein the tire pressure monitoring unit (3) contains a printed circuit board (33) which has a metal surface (36) and on which a measuring device for measuring a capacitive coupling of the metal surface (36) with a rim (1) of the wheel and control electronics are arranged, and wherein an electrical capacitance between the metal surface (36) and the rim (1) of the wheel is monitored by means of the tyre pressure monitoring unit (3), measurement signals correlating with the capacitance are compared with a standard range, and If measurement signals outside the normal range are detected, a warning signal is generated to indicate an impending wheel loss. [2] Method according to claim 1, characterized bythat in order to monitor the capacity, an alternating voltage is generated by the tire pressure monitoring unit (3) and applied to the metal part (36). [3] Method according to claim 2, characterized by that the alternating voltage has a frequency of at least 500 Hz, preferably at least 1 MHz. [4] Method according to claim 2 or 3, characterized by that the alternating voltage has a frequency of less than 10 MHz. [5] Method according to one of the preceding claims, characterized by that the normal range is determined from historical capacity measurement data. [6] Method according to one of the preceding claims, characterized by that the standard range is determined as a function of measurement signals from an acceleration sensor of the tire pressure monitoring unit (3). [7] Method according to one of the preceding claims, characterized by that the normal range is recalculated every time you start your journey. [8] Tire pressure monitoring unit for mounting on a vehicle wheel, with a pressure sensor for measuring the tire pressure, a transmitter for wireless transmission of tire pressure data, control electronics, an energy source (34), and a housing (32) in which the pressure sensor, the energy source (34), the transmitting device and the control electronics are arranged, characterized by a metal surface (36) and a measuring device for measuring a capacitive coupling of the metal surface (36) to a rim (1), wherein the metal surface (36) is integrated into a printed circuit board (33) on which the control electronics and the measuring device are arranged. [9] Tire pressure monitoring unit according to claim 8, characterized bya voltage divider formed from a first resistor (R1) and a second resistor (R2), a high-frequency generator (4) connected in series with the metal surface (36) via the first resistor (R1), and a voltmeter (AD) for measuring a voltage between the first resistor (R1) and the second resistor (R2).

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