Method for measuring and evaluating tire pressure with an assignment of wheel positions and tire pressure measuring system

Abstract

Method for measuring and evaluating tire pressure with an assignment of wheel positions (I, II, III, IV) of a vehicle (1) for evaluation in a tire pressure measuring system, wherein each wheel (2) of the vehicle (1) is assigned an air pressure monitoring device (10), an LF receiver (11), in particular a magnetic field strength receiver, an evaluation unit (13), an RF transmitter (12) and an individual wheel identifier, wherein the LF receiver (11) receives electrical LF signals from an LF transmitter (4) of a central unit (3) arranged in the vehicle (1), the evaluation unit (13) of each wheel (2) evaluates the signal strengths received from the LF transmitter (4) and determines a wheel speed from this, the RF transmitter (12) of the wheel (2) sends RF signals with information about the wheel speed and the individual wheel identifier to the central unit (3) of the vehicle (1), the central unit (3) determines the wheel position (I, II, III or IV) of the wheel (2) using another measuring device (7) and the central unit (3) assigns the air pressure control device (10) and its individual wheel identifier to the known wheel position (I, II, III or IV) on the vehicle (1).

Description

[0001] The present invention relates to a method for measuring and evaluating tire pressure with an assignment of wheel positions of a vehicle for evaluation in a tire pressure measuring system and a corresponding tire pressure measuring system for carrying out the method.

[0002] Modern vehicles are equipped with tire pressure monitoring systems (TPMS) that determine the current tire pressure and warn the driver if it deviates from a predetermined pressure. Such TPMS significantly contribute to vehicle safety.

[0003] Typical tire pressure monitoring systems (TPMS) are usually equipped with pressure sensors in the tires, which transmit the current air pressure to a central evaluation unit. Each wheel of the vehicle is assigned a TPMS, which transmits the information, along with an individual wheel identifier, to the evaluation unit. One challenge is ensuring that the data transmission is largely free of interference. Furthermore, a particular problem arises from the fact that the TPMS must be assignable to a specific wheel position. If this were not the case, the driver could not be informed of a problem at a particular wheel position. However, if a wheel is changed and potentially mounted in a different position on the vehicle, a reliable assignment of the TPMS of the corresponding wheel to a specific wheel position on the vehicle would no longer be possible.To eliminate this source of error, systems for assigning air pressure monitoring devices to specific wheel positions and their wheel recognition have been described in the prior art.

[0004] For example, EP 0 806 307 A2 discloses sensors that use energy generated solely by wheel rotation to determine the current rotational speed of the wheel and transmit this information to an associated receiver. The current rotational speed of each wheel is then transmitted to a central unit via a cable between the receiver and a central processing unit. A disadvantage of this method is the relatively high cost of wiring the receivers and their corresponding susceptibility to interference.

[0005] From EP 1 807 270 B1, a wheel detection system is known which uses radio frequency signals and a received signal strength that varies periodically due to the wheel's rotation to determine the current rotational speed of the wheel. A disadvantage of this system is that the radio frequency is susceptible to interference, as reflections from the environment can cause interference and signal cancellation. This makes it difficult to determine the periodicity of the signals and, consequently, the wheel rotational speed.

[0006] From DE 101 44 360 A1, a method is known in which tire pressure measuring devices are assigned to wheel positions during a vehicle cornering. For this purpose, the ABS determines whether the curve is left or right. Then, wheel rotational speeds are measured in each tire and sent, along with identifiers, to a central evaluation unit. There, the wheel rotational speeds are correlated with the curve information determined by the ABS. The two higher wheel rotational speeds are assigned to the side of the vehicle on the outside of the curve, and the two lower wheel rotational speeds are assigned to the other side of the vehicle.

[0007] WO 2008 / 009910 A1 describes a method for identifying faulty speed sensors using an alternative sensor. If the alternative sensor indicates that the wheel is rotating and a speed sensor does not, the faulty speed sensor is identified. The alternative sensor comprises at least one pressure sensor connected to a tire of the vehicle.

[0008] The object of the present invention is therefore to create a method for measuring and evaluating tire pressure with an assignment of wheel positions of a vehicle for evaluation in a tire pressure measuring system, as well as a tire pressure measuring system for carrying out the method, which is both simple and cost-effective in its construction and has a particularly high interference immunity.

[0009] The problem is solved using a method and a tire pressure measuring system according to the independent claims.

[0010] The method according to the invention serves for tire pressure measurement and evaluation, assigning wheel positions of a vehicle to a tire pressure monitoring system. Each wheel of the vehicle is assigned a tire pressure monitoring device, a low-frequency (LF) receiver (in particular a magnetic field strength receiver), an evaluation unit, a radio-frequency (RF) transmitter, and an individual wheel identifier. The LF receiver receives electrical LF signals from an LF transmitter located in a central unit within the vehicle. The evaluation unit of that wheel evaluates the received signal strengths and determines the wheel speed. The wheel's transmitter then sends RF signals containing information about the determined wheel speed and the individual wheel identifier to the vehicle's central unit.The central unit then determines the wheel position using another measuring device, so that the central unit can assign the tire pressure monitoring device and its individual wheel identifier to the known wheel position on the vehicle.

[0011] In a particularly advantageous embodiment of the method, the wheel positions are determined by comparing the wheel speed of the wheel identified via its wheel identifier, transmitted to the central unit, with the wheel speeds of known positions of another measuring device, in particular an anti-lock braking system (ABS system). If the transmitted wheel speeds closely match one of the wheel speeds of the other measuring device, the central unit assigns the corresponding tire pressure monitoring device and its individual wheel identifier to the known wheel position on the vehicle.

[0012] Alternatively, the assignment can also be made by comparing the transmitted wheel speeds of all four wheels. For this purpose, the type of curve, in particular whether it is a right or left turn, is first determined using the measuring device. The measuring device can be, in particular, a steering angle sensor, a gyroscope, or the turn signal. Since all four wheels have different turning radii when cornering, the central unit can deduce the position of each wheel on the vehicle by comparing the transmitted wheel speeds with each other, depending on the type of curve.

[0013] Low-frequency refers to long waves in the lower wavelength range, with frequencies between approximately 20 and 150 kilohertz. Radio-frequency, on the other hand, refers to frequencies greater than 100 megahertz. Due to the long wavelength of low-frequency signals, virtually no interference occurs, making it easier and less prone to detecting the periodicity of wheel rotation. However, the transmission of signals from the tire pressure monitoring system to the vehicle's central control unit is achieved using radio-frequency signals, which allow for more reliable data transmission.

[0014] The advantage of the method according to the invention is that no cabling is required from the central unit of the vehicle to the vicinity of the wheels in order to place the signals that are emitted or are to be emitted near the wheel.

[0015] In an advantageous embodiment of the method, the tire pressure monitoring device is activated either to perform wheel position detection or to receive the transmission of the tire pressure measured in the wheel via LF signals from the central unit. The tire pressure monitoring device includes, among other things, pressure sensors that measure the current tire pressure in the wheel and transmit it to the evaluation unit of the tire pressure monitoring device or to the RF transmitter. From there, the current tire pressure, along with the wheel identification, is sent to the vehicle's central unit via RF signals.

[0016] In an advantageous embodiment of the invention, the LF signals are also used to synchronize the air pressure control device.

[0017] If the wheel's rotational speed is determined from the periodically changing signal strength of the detected LF signal, the wheel can be individually assigned to a specific position within the vehicle. Particularly during vehicle operation, each wheel exhibits variations in rotational speed compared to the other wheels. This is due to the fact that a vehicle rarely travels in a perfectly straight line, but rather always navigates curves to a greater or lesser degree by making slight steering movements. The individual rotational speed of the wheel is determined by the periodically changing signal strength of the detected LF signal. The received signal strength changes periodically due to the wheel's rotation. Because the signal receiver is mounted at a specific point on the wheel and rotates around the wheel's axis, its position relative to the LF transmitter is constantly changing.This results in a change in the received signal strength, which allows conclusions to be drawn about the rotational speed of the wheel.

[0018] Once a specific wheel position is assigned to a specific tire pressure monitoring device with its wheel identifier, all subsequent signals sent from this device to the vehicle's central control unit that also contain this wheel identifier are automatically assigned to the corresponding wheel position on the vehicle. This eliminates the need to assign a wheel identifier and position for every signal transmission.

[0019] It is particularly advantageous to assign the wheel position while the vehicle is cornering. Especially during cornering, significantly different wheel speeds are observed. This makes it particularly easy to identify the individual wheel speeds and their corresponding wheel positions.

[0020] To ensure that the wheel identifier continues to correspond to the wheel position, it is advantageous for the wheel position to be reassigned to the wheel identifier after predetermined events. Such events could include, for example, the ignition being switched on, a certain time elapsed since the last assignment, a tire change detected by the system, a certain distance driven, or other similar events.

[0021] A tire pressure monitoring system according to the invention for carrying out the method comprises a central unit arranged in the vehicle with a (low-frequency) LF transmitter, a (radio-frequency) RF receiver, and a central evaluation unit. At each wheel of the vehicle, a tire pressure monitoring device, a (low-frequency) LF receiver, a (radio-frequency) RF transmitter, and an evaluation unit for determining the rotational speed based on a periodically changing strength of the received (low-frequency) LF signal from the LF transmitter are arranged. Furthermore, the tire pressure monitoring system comprises a measuring device for measuring the wheel rotational speed at each wheel and / or for determining the curve type.

[0022] To compare the wheel speed determined by the frequency of the low-frequency (LF) transmitters and receivers with the wheel speed at a known wheel position on the vehicle, a particularly preferred embodiment provides a stationary measuring device at each wheel position to determine the wheel speed there. The central unit communicates with the radio-frequency (RF) transmitter on the wheel and also with the stationary measuring device located at a known wheel position. The resulting data allows for a comparison and thus an assignment of the signals from the wheel to a specific wheel position. Following this assignment, the tire pressure monitoring device is initialized and / or synchronized via the low-frequency transmitters and receivers, and the tire pressure detected by the tire pressure monitoring device is transmitted via the radio-frequency transmitters and receivers.

[0023] Preferably, the low-frequency receiving device is a magnetic field strength receiver. The rotational speed of the wheel causes a change in the magnetic field strength of the low-frequency signal, thereby allowing a periodicity to be detected which permits inferences about the actual rotational speed.

[0024] Preferably, the low-frequency receiver, the radio-frequency transmitter, and the evaluation unit are integrated into the tire pressure monitoring device. The tire pressure monitoring device can be mounted on the wheel as a single component.

[0025] Further advantages of the invention are described in the following exemplary embodiments. It shows: Fig. 1 a schematic representation of a vehicle, Fig. 2 a schematic representation of a curve movement of the vehicle and Fig. 3 a periodically changing signal strength at different wheels.

[0026] Fig. Figure 1 shows a schematic representation of a vehicle 1 with four wheels 2. A central unit 3 is arranged in the vehicle 1, which includes a low-frequency (LF) transmitter 4 and a radio-frequency (RF) receiver 5. The central unit 3 also has a central evaluation unit 6. Measuring devices 7a, connected here by a line 8, are mounted at each wheel 2 and are connected to the central evaluation unit 6. The measuring device 7a determines the rotational speed of its respective assigned wheel 2. It can be part of another monitoring system, such as an anti-lock braking system (ABS) or an electronic stability program (ESP).

[0027] Each wheel 2 is equipped with a tire pressure monitoring device 10. The tire pressure monitoring device 10 consists, for example, of a pressure sensor that measures the tire pressure. Each wheel 2 is also equipped with a low-frequency (LF) receiver 11 and a radio-frequency (RF) transmitter 12. The tire pressure monitoring device 10, LF receiver 11, and RF transmitter 12 are connected to an evaluation unit 13. In the evaluation unit 13, the signal received by the LF receiver 11 from the LF transmitter 4 is evaluated. As soon as the wheel 2 rotates, the received strength of the LF signal changes, resulting in a periodically changing signal strength. This periodicity is used to infer the rotational speed of the respective wheel. This is done either by counting the received minimum signal strengths or the received maximum signal strengths.Alternatively, the average signal strength can be determined and compared with the number of times the actual signal strength matches the average signal strength. These matches also allow for a determination of the actual rotational speed of wheel 2. Another possibility is to perform a Fast Fourier Transform on the received signal strength and deduce the current rotational speed of the wheel from this.

[0028] The rotational speed of wheel 2 determined by the evaluation unit 13 is sent via the RF transmitter 12 to the RF receiver 5 of the central unit 3 using radio frequency in the range above 100 megahertz.

[0029] The long-wavelength transmission of signals from the LF transmitter 4 of the central unit 3 to the LF receiver 11 on the wheel 2 occurs at a frequency in the range of approximately 20 to 150 kilohertz. The precise frequency range specified for low frequency and radio frequency is not essential here. What is more important is that the signal for determining the rotational speed has a longer wavelength and is therefore less susceptible to reflections and interference than the transmission of the rotational speed data and, subsequently, the pressure signals in the respective wheel 2 to the central unit 3. The shorter wavelength of the radio frequency is used for more precise data transmission compared to the longer wavelength of the low frequency.

[0030] To assign each wheel 2 to a specific position on the vehicle, the rotational speed of the wheel 2 transmitted by the RF transmitter 12 is evaluated in the central unit 3. For this purpose, the central evaluation unit 6 receives data regarding the rotational speed of a wheel 2 at a given position from the stationary measuring device 7a located on each wheel 2 via a line 8. The central evaluation unit 6 compares the signals received by the RF receiver 5 regarding the rotational speed of the respective wheels 2 and compares these with the rotational speeds of the wheels 2 transmitted by the measuring devices 7a at specific positions. As soon as a close match of the transmitted wheel rotational speeds is detected, the ID wheel identifier transmitted by the RF transmitter 12 of the respective wheel 2 is assigned to the specific position of the wheel on the vehicle.The system thus recognizes, based on the transmitted ID identifier, which wheel position the received signals represent in subsequent signal transmissions from the respective RF transmitter 12.

[0031] Alternatively, the wheel position can also be determined by comparing the transmitted wheel rotation speeds of all four wheels 2 with each other. For this purpose, a measuring device 7b, as described in Fig. The type of curve is determined by the measuring device 7b, which is visibly connected to the steering wheel 14. The key distinction here is between a left and a right turn. The measuring device 7b can be, in particular, a steering angle sensor, a gyroscope, or the turn signal. Since all four wheels 2 traverse different but characteristic curve radii when cornering, the central unit 3 can, by comparing the transmitted wheel rotation speeds with each other depending on the type of curve, deduce the position of each wheel 2 on the vehicle 1.

[0032] In order for the evaluation unit 13 of the respective wheels 2 to recognize that it should perform a speed determination, a corresponding signal, possibly together with a signal for system synchronization, is also detected via the low frequency of the LF transmitter 4 and the LF receiver 11. Upon receiving a corresponding LF signal from the central unit 3, the evaluation unit 13 is thus activated to perform a speed determination.

[0033] Preferably, the LF receiver 11 on the respective wheel 2 is a magnetic field strength receiver. Particularly with the low-frequency signals used, it is sufficient to evaluate only the magnetic field strength. This results in a slowly changing magnetic field that is largely insensitive to interference. Determining the periodicity of the wheel rotation is therefore relatively simple.

[0034] The LF receiver 11, the RF transmitter 12, and the evaluation unit 13 can form a single unit together with the air pressure monitoring device 10. This allows for very simple and protected mounting on the wheel 2. The LF transmitter 4 and the RF receiver 5 can also be integral components of the central unit 3. Of course, it is also possible for them to be located outside the central unit 3. In any case, it is essential that a separate transmitter 4 or receiver 5 is not provided for each wheel, but rather that the LF transmitter 4 and RF receiver 5 are centrally located for all wheels 2 of the vehicle 1.

[0035] In Fig. Figure 2 shows a top view of vehicle 1 during a turn. The respective concentric circles indicate the paths of the individual wheels 2 at the respective positions of vehicle 1. It is evident that the wheel at position I travels the largest turning radius, while the wheel at position III has the smallest turning radius. Therefore, the wheel 2 at position I must have the highest rotational speed, while the wheel 2 at position III has the lowest. The wheels 2 at positions II and IV also differ in their rotational speed and turning radius, although this is not as pronounced as with the wheels 2 at positions I and III. This illustration shows that a turn is particularly advantageous for determining the rotational speed of the wheels 2 at the respective positions, as this is when the differences in the rotational speed of the individual wheels 2 of vehicle 1 are most apparent.

[0036] In Fig. 3 is the change of the position of the respective wheel at positions I to IV of vehicle 1. Fig.Figure 2 shows that the signal strength change has the highest frequency at position I. It is therefore concluded that the highest wheel speed also occurs here. The wheel speed is determined, for example, by counting the respective amplitudes or by other methods described previously. The lowest frequency of the signal strength change is observed at position III. Thus, the lowest wheel speed occurs here. This wheel speed is followed by the speed at position II and then position IV. By calculating the respective wheel speed and transmitting this speed along with the ID identifier of the respective wheel 2, the central unit 3 compares the values ​​with those of the measuring device 7, whose position on the vehicle 1 is known and fixed, to assign the ID identifier of wheel 2 to the specific positions I to IV on the vehicle 1.Further signals, which are sent to the central unit 3 together with the ID identifier of wheel 2, can thus be assigned exactly to a specific position I to IV on the vehicle 1.

[0037] The rotational speed at each position (I to IV) can be determined with every signal transmission regarding the current air pressure in wheel 2. However, it is usually sufficient to transmit the rotational speed and thus wheel position only for certain specific events. Such events could include, for example, switching on the vehicle's ignition or manual input indicating that a tire change has taken place. Of course, other events can also be selected to determine the rotational speed and thus the position.

[0038] The present invention is not limited to the illustrated embodiments. Modifications of the invention within the scope of the claims are possible at any time. Reference symbol list 1 vehicle 2 wheel 3 Central unit 4 LF transmitters 5 RF receivers 6 Central evaluation unit 7 Measuring device 8 Line 10 Air pressure monitoring device 11 LF receivers 12 RF transmitters 13 Evaluation unit 14 Steering wheel Wheel positions I, II, III, IV

Claims

[1] Method for measuring and evaluating tire pressure with an assignment of wheel positions (I, II, III, IV) of a vehicle (1) for evaluation in a tire pressure measuring system, wherein each wheel (2) of the vehicle (1) is assigned an air pressure monitoring device (10), an LF receiver (11), in particular a magnetic field strength receiver, an evaluation unit (13), an RF transmitter (12) and an individual wheel identifier, wherein the LF receiver (11) receives electrical LF signals from an LF transmitter (4) of a central unit (3) arranged in the vehicle (1), the evaluation unit (13) of each wheel (2) evaluates the signal strengths received from the LF transmitter (4) and determines a wheel speed from this, the RF transmitter (12) of the wheel (2) sends RF signals with information about the wheel speed and the individual wheel identifier to the central unit (3) of the vehicle (1), the central unit (3) determines the wheel position (I, II, III or IV) of the wheel (2) using another measuring device (7) and the central unit (3) assigns the air pressure control device (10) and its individual wheel identifier to the known wheel position (I, II, III or IV) on the vehicle (1). [2] Method according to the previous claim, characterized by , that the central unit (3) to determine the wheel position (I, II, III or IV) of the wheel (2) compares the transmitted wheel speed with the wheel speeds of known positions of the other measuring device (7), in particular an ABS system, and if there is a high degree of agreement between two wheel speeds, the central unit (3) assigns the transmitted wheel identifier of the wheel (2) to a known position of the measuring device (7). [3] Method according to one or more of the preceding claims, characterized by, that the central unit (3) to determine the wheel position (I, II, III or IV) of the wheel (2) compares the transmitted wheel rotation speeds of all four wheels (2) with each other, and the central unit (3) assigns the transmitted wheel identifier of the wheel (2) to a wheel position (I, II, III or IV) depending on the type of curve, in particular right or left curve, wherein the type of curve is determined by means of the measuring device (7), in particular a steering angle sensor, a gyroscope or the turn signal operation. [4] Method according to one or more of the preceding claims, characterized by , that the air pressure control device (10) or the determination of the position (I, II, III, IV) is started by means of the LF signals from the central unit (3). [5] Method according to one or more of the preceding claims, characterized by , that the air pressure control device (10) is synchronized by means of the LF signals from the central unit (3). [6] Method according to one or more of the preceding claims, characterized by , that the rotational speed of the wheel (2) is determined from the periodically changing signal strength of the detected LF signal. [7] Method according to one or more of the preceding claims, characterized by , that the wheel position determined in each case (I, II, III, IV) is also assigned to all other signals of the air pressure control device (10) of the same wheel identification by the central unit (3). [8] Method according to one or more of the preceding claims, characterized by , that the assignment of the wheel position (I, II, III, IV) takes place during a cornering maneuver of the vehicle (1). [9] Method according to one or more of the preceding claims, characterized by, that a reassignment of the wheel position (I, II, III, IV) to the wheel identifier takes place after predetermined events, for example, switching on the ignition of the engine, time since the last assignment, tire change, mileage or other events. [10] Tire pressure measuring system for carrying out the method according to one or more of the preceding claims, with a central unit (3) arranged in a vehicle (1) with an LF transmitter (4), an RF receiver (5) and a central evaluation unit (6), with an air pressure monitoring device (10), LF receiver (11), RF transmitter (12) and evaluation unit (13) arranged at each wheel (2) of the vehicle (1) for determining a rotational speed based on a periodically changing strength of the LF signal received by the LF transmitter (4) and a measuring device (7) for measuring the wheel rotational speed at each wheel (2) and / or for determining the type of curve. [11] Tire pressure measuring system according to claim 10, characterized by , that the measuring device (7) is arranged stationary at each wheel position (I, II, III, IV). [12] Tire pressure measuring system according to one of claims 10 or 11, characterized by , that the LF receiving device (11) is a magnetic field strength receiver. [13] Tire pressure measuring system according to one or more of claims 10 to 12, characterized by, that the LF receiver (11), the RF transmitter (12), the evaluation unit (13) and the air pressure control device (10) and / or the LF transmitter (4), the RF receiver (5) and the central evaluation unit (6) are each a single unit.

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