JP2006250663A - Tire strain measuring system by rfid sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire strain measuring system by an RFID (Radio Frequency Identification) sensor capable of measuring the tire strain with an inexpensive system constitution having a simple structure without using a battery. <P>SOLUTION: This system is constituted as follows: a sensor unit, which is built in a tire, comprising a magnetometric sensor for detecting the tire strain by a resistance value change, a magnet for changing the resistance value of the magnetometric sensor corresponding to the strain quantity, and the RFID sensor for transmitting information by connecting the magnetometric sensor; a reader, which is disposed in each tire house, for communicating by radio with the RFID sensor in the sensor unit, and reading from a response signal measurement data comprising data acquired by converting ID information from the RFID sensor and resistance value into electric signals and scaling them; and an operation control device for measuring the strain of each tire by performing operation processing of the measurement data acquired from each reader and a monitor for informing a driver of tire strain information. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a tire distortion measurement system that measures tire distortion of a pneumatic rubber tire (hereinafter simply referred to as a tire) equipped in a vehicle using an RFID (Radio Frequency Identification) sensor. The RFID sensor refers to an RFID tag in which a sensor interface circuit is built in the RFID tag and an external terminal for connecting the sensor is provided.

  Conventionally, there are anti-lock brake systems (ABS) and traction control systems in order to prevent accidents such as slipping due to a sudden stop or hydroplaning that occurs when the road surface is wet due to rain. The ABS is a system that detects the rotational state of each tire and controls the braking force so as to prevent each tire from entering a locked state based on the detected data. Here, as the rotation state of the tire, the rotation speed, air pressure, strain, and the like of each tire are detected, and the detection data is analyzed by a control device to control the braking force.

  Many proposals have been made as methods for detecting the rotational speed, air pressure, strain, and the like of each of the tires described above. As an example, Japanese Unexamined Patent Application Publication No. 2004-102753 “Tire Condition Detection Device, Sensor Unit and Tire, and In the "vehicle braking control apparatus", a sensor unit is fixed to a rim in a tire, and detection data obtained by an acceleration sensor or a pressure sensor in the sensor unit is processed by a CPU or a peripheral analog circuit. A method for detecting the state of a tire by performing wireless communication with a monitor device fixed to a tire house using electromagnetic waves is disclosed.

In “Tire condition monitoring device” of Japanese Patent Application Laid-Open No. 2004-155222, a transmitter is fixed to a wheel in a tire, and detection data obtained by an acceleration sensor or a pressure sensor in the transmitter is constituted by a microcomputer. A method of detecting the state of a tire by performing wireless communication with a receiver that is processed by a transmission controller and fixed to a vehicle body is disclosed.
JP 2004-102753 A JP 2004-155222 A

  However, in the above Japanese Patent Application Laid-Open No. 2004-102753, it is described that the analog circuit power source, the CPU driving power source, and the oscillation circuit power source for processing the sensor signal are obtained by rectifying the electromagnetic wave of the carrier. The electric power obtained by the method is only about several hundred μW even when the distance between the sensor unit and the monitor device is about 15 cm, and even when the CPU drive voltage is 3 V, only a current supply capability of about 100 μA can be obtained. Therefore, it is impossible to oscillate the frequency in the microwave band with such a minute power, drive the CPU or peripheral analog circuit, and further transmit electromagnetic waves.

  In addition, in the above Japanese Patent Application Laid-Open No. 2004-155222, it is described that the power supply for the communication controller and the power supply for the transmission circuit for processing the sensor signal are supplied by the power from the battery. It cannot be used for a long time. Therefore, it is necessary to periodically replace the battery in the tire, which is not realistic.

  The present invention has been made to solve the above-described problems, and is structurally simple without using a battery as a driving power source for an RFID sensor and a strain measurement sensor connected to the RFID sensor. Another object of the present invention is to provide a tire strain measurement system using an RFID sensor, which can measure tire strain with a low-cost system configuration.

  In order to solve the above problems, in the tire strain measurement system using an RFID sensor according to the present invention, a magnetic sensor for detecting tire strain by a change in resistance value in a tire mounted on the front, rear, left, and right of the vehicle, and the amount of strain. A sensor unit including a magnet for changing the resistance value of the magnetic sensor and an RFID sensor for connecting the magnetic sensor to transmit information, and wirelessly connected to the RFID sensor of the sensor unit in each tire house. A reader is provided to read the measurement data consisting of the scaled data by converting the ID information and resistance value of the RFID sensor into a voltage signal from the response signal, and processing the measurement data obtained from each reader. The calculation control device for measuring the strain of each tire and the driver is notified of tire strain information. Configure a monitor.

  As a drive power source for the RFID sensor and the magnetic sensor, a circuit power source that rectifies and stabilizes the induced electromotive force generated in the antenna by the electromagnetic field or electromagnetic wave output from the reader, and the power accumulated in the large-capacity charging capacitor use.

  The magnetic sensor is a magnetoresistive (MR) element.

  The arithmetic and control unit is capable of controlling each of the brake braking device and the engine control unit based on the measured change in tire strain data.

  If the vehicle is equipped with the tire strain measurement system using the RFID sensor of the present invention, a magnetic sensor for detecting tire strain by a change in resistance value as a sensor unit, and an RFID for transmitting information by connecting the magnet and the magnetic sensor. Consists of sensors, the induced electromotive force generated by electromagnetic fields or electromagnetic waves can be used as a circuit power supply, and the power stored in the charging capacitor can be used, eliminating the need for a sensor system battery and making the tire distortion structurally simple and inexpensive With such a system, it is possible to achieve a great effect that measurement can be performed stably for a long period of time.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 is a layout diagram of a tire strain measurement system using an RFID sensor according to the present invention. Tire strain is caused by resistance value changes in tires 2 mounted on front, rear, left and right (FL, FR, RL, RR) of a vehicle 6. Built-in sensor unit 1 comprising a magnetoresistive element for detection, a magnet for changing the resistance value of the magnetoresistive element according to the amount of strain, and an RFID sensor for connecting the magnetoresistive element to transmit information To do.

  Further, a reader for reading measurement data comprising data scaled by converting ID information and resistance value of the RFID sensor into a voltage signal from the response signal by performing wireless communication with the RFID sensor of the sensor unit 1 in each tire house. 3 is provided, an arithmetic control device 4 for calculating the measurement data obtained from each reader 3 to measure the distortion of each tire 2, and a monitor 5 for informing the driver of tire distortion information. To do. The monitor 5 may be a monitor of a car navigation system without being a dedicated monitor.

  FIG. 2 is a schematic block diagram of a sensor unit in a tire strain measurement system using an RFID sensor of the present invention. A magnetoresistive element 18 is connected as a magnetic sensor to an RFID sensor configured by connecting an antenna 7 to an RFID chip 8. Constitute. An antenna 7 for communicating with a reader by electromagnetic field or electromagnetic wave is connected to a tuning circuit 9 composed of a tuning capacitor (not shown) to constitute a resonance circuit. The antenna 7 is generally a loop antenna, and it is preferable to use a high-efficiency antenna material capable of obtaining a large mutual inductance for the conductor of the loop antenna. The magnetoresistive element 18 includes various types such as GMR (Giant Magneto Resistance Effect) and TMR (Tunneling Magneto Resistance Effect), but is not particularly limited.

  In the subsequent stage of the tuning circuit 9, the voltage waveform of the induced electromotive force generated when the electromagnetic field or electromagnetic wave output from the reader passes through the antenna 7 is detected, or the induced electromotive force is half-wave or full-wave rectified. The rectifier circuit 10 for taking out the DC voltage is connected. A diode (not shown) used in the rectifier circuit 10 is preferably a diode having a low forward voltage drop, such as a Schottky barrier diode.

  Next, after the rectifier circuit 10, a clock generation circuit 11 for dividing the detected carrier to generate a system clock, and performing a demodulation operation for extracting a signal from the carrier at the time of signal reception or at the time of signal transmission A modulation / demodulation circuit 12 for performing a modulation operation by a switching element (not shown) in FIG. 5 and a power supply circuit 13 for stabilizing the DC voltage and supplying a circuit power supply or supplying a charging voltage to the charging capacitor 14 are provided. Connecting. The charging capacitor 14 is preferably a large-capacity electric double layer capacitor, but other capacitors may be selected according to the current consumption.

  Next, the modulation / demodulation circuit 12 is followed by SiRAM (Sensor Interface RAM), which is a ferroelectric memory, which is accessible by the processing unit required by the sensor. A logic circuit 15 for performing writing or reading control of ID information or measurement data on the trademark 16 and A for converting a resistance value of the magnetoresistive element 18 into a voltage signal and converting a scaled analog signal into a digital signal. / D conversion circuit 17 etc. are connected.

  FIG. 3 is a block diagram of the first embodiment of the A / D conversion circuit of FIG. 2. The resistance value of the magnetoresistive element 18 is converted into a voltage signal and input to the analog input circuit 20. The analog input circuit 20 is composed of an OP amplifier, a resistor and the like for scaling the input voltage to an appropriate level. As a power source for the magnetoresistive element 18, a circuit power source obtained from the power source circuit 13 of the RFID chip 8 is used. In FIG. 3, the number of inputs is 3 channels, but there is no particular limitation.

  Next, an analog multiplexer 21 for sequentially switching and inputting the voltage signal output from the analog input circuit 20 to the A / D converter 22 is connected to the subsequent stage of the analog input circuit 20, and the A / D converter In 22, the voltage signal which is an analog signal is converted into a digital signal. Here, when the output of the A / D converter 22 is a serial output type, it is input to the shift register 23 in synchronization with the system clock and converted into parallel data, and then written to the SiRAM 16. In addition, when the output of the A / D converter 22 is a parallel output type, writing to the SiRAM 16 is performed in synchronization with the system clock. The resolution of the A / D converter 22 may be arbitrary in the range of about 4 to 16 bits.

  FIG. 4 is a block diagram of the second embodiment of the A / D conversion circuit of FIG. 2, and converts the resistance value of the magnetoresistive element 18 into a voltage signal and converts it to the analog input circuit 20 as in the first embodiment. input. The analog input circuit 20 is composed of an OP amplifier, a resistor and the like for scaling the input voltage to an appropriate level. As a power source for the magnetoresistive element 18, a circuit power source obtained from the power source circuit 13 of the RFID chip 8 is used. In FIG. 4, the number of inputs is 3 channels, but there is no particular limitation.

  Next, an A / D converter 22 is independently connected to each magnetoresistive element 18 at the subsequent stage of the analog input circuit 20, and the A / D converter 22 converts a voltage signal into a digital signal. The output of the A / D converter 22 is connected directly to a specific address of the SiRAM 16 as a parallel output type, and is directly written to the specific address of the SiRAM 16 in synchronization with the system clock. In addition, the detection data at a specific address is directly read by an output command from the reader. According to this method, coupled with the original high-speed operation of the SiRAM 16, further detection data can be written or read at a high speed.

  The SiRAM 16 is a non-volatile memory, and ID information and detection data are not lost even when the circuit power is turned off. For this reason, unlike the DRAM, a refresh operation is unnecessary, and the power consumption is much less than that of the DRAM. Further, since the data write voltage does not need to be boosted to a high voltage unlike an EEPROM or a flash memory, the booster circuit is simplified. Furthermore, the writing or reading speed is equivalent to that of DRAM, and is much faster than EEPROM and flash memory.

  FIGS. 5A and 5B are attachment position diagrams of the sensor unit in the tire, in which FIG. 5A is a cross-sectional view and FIG. Moreover, the state which embed | buried and attached the sensor unit 1 to the tread inner surface of the tire 2 is shown. In the case of detecting longitudinal distortion in the magnetoresistive element 18 and magnet 19 constituting the magnetic sensor of the sensor unit 1, the magnetoresistive element 18 and magnet 19 are arranged in the longitudinal direction to detect lateral distortion. The magnetoresistive element 18 and the magnet 19 are arranged in the vertical direction. Although three places of a center part and both side parts are suitable for an arrangement | positioning location, it does not specifically limit. Further, when detecting strain in both directions, the sensor unit 1 for detecting longitudinal strain and detecting strain in the lateral direction is arranged at each position.

  FIG. 6 is a schematic block diagram of a reader. The reader 3 includes a transmission / reception circuit 25 for performing wireless communication with the RFID sensor of the sensor unit 1 via an antenna 24, and a signal generation circuit 26 for generating a carrier signal. And a communication interface circuit 28 for transmitting measurement data obtained from the response signal to the arithmetic and control unit 4, a control circuit 27 for controlling the transmission / reception circuit 25, the signal generation circuit 26, and the communication interface circuit 28, and the like. To do.

  FIG. 7 is a schematic block diagram of the arithmetic and control unit, and a communication interface circuit 29 for receiving measurement data transmitted from each reader 3 and for measuring the distortion of the tire 2 by calculating and analyzing the measurement data. An arithmetic circuit 30, an output circuit 32 for performing monitor output to inform the driver of tire strain information of each tire 2 on the monitor 5, and each of the brake braking device and the engine control device based on changes in the tire strain data The control circuit 31 is configured to perform control.

  FIG. 8 is a data read position relationship diagram between the reader and the sensor unit of the tire strain measurement system using the RFID sensor of the present invention. The antenna 24 of the reader 3 provided in the tire house 33 and the inner surface of the tread of the tire 2 are embedded. Between the fixed antennas 7 of the sensor unit 1, wireless communication is performed at three points of the point B before kicking, the point C during kicking, and the point D after kicking, and the distortion of the tire 2 is measured. Here, when the tire 2 is rotated in the direction of the arrow in the drawing, the position of the antenna 24 of the reader 3 is a point A that is 180 degrees opposite to the point B before kicking out of the tire 2 is the maximum point of the response signal reception level. Position. The point C during kicking is when the outer tread surface of the sensor unit 1 is in maximum contact with the road surface, and the point D after kicking is substantially symmetrical with the point B before kicking around the point C during kicking. Position.

  Embodiments of the present invention will be described with reference to the drawings.

  First, as shown in FIGS. 1 and 8, the sensor unit 1 is built in a tire 2 mounted on the front, rear, left and right (FL, FR, RL, RR) of the vehicle 6. As shown in FIG. 2, the sensor unit 1 includes a magnetoresistive element 18 for detecting tire strain by a change in resistance value, a magnet 19 for changing the resistance value of the magnetoresistive element 18 according to the amount of strain, and the magnetism. The antenna 7 for transmitting information by connecting the resistance element 18 is constituted by an RFID sensor connected to the RFID chip 8. The mounting position of the sensor unit 1 is embedded or fixed to the inner surface of the tread of the tire 2 as shown in FIG. Moreover, the leader 3 is arranged in each tire house 33, and each leader 3 and the arithmetic and control unit 4 are connected. Further, the arithmetic control device 4 and the monitor 5 are connected.

  Next, when the vehicle 6 travels and measures the distortion of the tire 2, the distortion at the three points of the point B before kicking, the point C during kicking, and the point D after kicking is measured between the leader 3 and the sensor unit 1. To do. In this measurement, the vehicle speed can be calculated by measuring the passage period T of the sensor unit 1 that passes the maximum point A of the reception level of the response signal, and the position of T / 2 hours after the sensor unit 1 passes the point A is It becomes point B before kicking, and the position at T / 2 + Δt1 time becomes point C during kicking, and further, the position at time T / 2 + 2Δt1 becomes point D after kicking. The Δt1 is obtained from the vehicle speed.

  Here, the principle of the distortion measurement of the tire 2 will be described.

  When the tire 2 changes in strain acceleration due to a decrease in air pressure, slip, or the like, the magnet 19 expands or contracts or bends according to the amount of strain, as indicated by arrows at the magnetoresistive element 18 and the magnet 19 in FIGS. The magnetic resistance element 18 is changed in magnitude of the magnetic field. The magnetoresistive element 18 is a sensor whose resistance value changes with a change in the magnitude of the magnetic field, and the resistance value changes according to the amount of strain. For this reason, when the tire 2 is distorted due to a decrease in air pressure, slip, or the like, the measurement data of the A / D conversion circuit 17 connected to the magnetoresistive element 18 is changed and measured. The measurement data is always detected and read by the reader 3 together with the unique ID information of the sensor unit 1. Furthermore, the distortion of the tire 2 can be measured by calculating and analyzing the measurement data obtained from the reader 3 by the calculation control device 4.

  And the distortion data of the tire 2 at the normal time and the distortion data of the tire 2 measured in real time are compared, and when the data different from the normal data is obtained, the tire distortion information is displayed on the monitor 5 according to the state. The driver can be informed and danger avoidance can be promoted.

  In addition to displaying the tire distortion information on the monitor 5, the brake control signal based on the change in the tire distortion data is transmitted to a brake braking device (not shown), so that the brake control can be automatically performed. By transmitting an engine control signal based on the change of the distortion data to an engine control device (not shown), the engine can be automatically controlled.

  The tire strain measurement system using an RFID sensor according to the present invention is intended for a vehicle equipped with a general pneumatic rubber tire, for example, a passenger car or a truck. However, any type of vehicle or device may be used as long as it is equipped with a pneumatic rubber tire. It does not matter.

It is an arrangement block diagram of a tire distortion measuring system by an RFID sensor of the present invention. It is a schematic block diagram of the sensor unit in the tire distortion measuring system by the RFID sensor of the present invention. FIG. 3 is a block diagram of a first embodiment of the A / D conversion circuit of FIG. 2. It is a block diagram of 2nd embodiment of the A / D conversion circuit of FIG. It is an attachment position figure of a sensor unit in a tire. It is a schematic block diagram of a leader. It is a schematic block diagram of an arithmetic and control unit. It is a reading positional relationship figure of the data between the reader of the tire distortion measurement system by the RFID sensor of the present invention, and a sensor unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sensor unit 2 Tire 3 Reader 4 Arithmetic controller 5 Monitor 6 Car 7 Antenna 8 RFID chip 9 Tuning circuit 10 Rectification circuit 11 Clock generation circuit 12 Modulation / demodulation circuit 13 Power supply circuit 14 Charging capacitor 15 Logic circuit 16 SiRAM
17 A / D conversion circuit 18 Magnetoresistive element 19 Magnet 20 Sensor input circuit 21 Analog multiplexer 22 A / D converter 23 Shift register 24 Antenna 25 Transmission / reception circuit 26 Signal generation circuit 27 Control circuit 28 Communication interface circuit 29 Communication interface circuit 30 Arithmetic circuit 31 Control circuit 32 Output circuit 33 Tire house

Claims (4)

  A magnetic sensor for detecting tire distortion based on a change in resistance value, a magnet for changing the resistance value of the magnetic sensor according to the amount of distortion, and the magnetic sensor are connected in tires mounted on the front, rear, left and right of the vehicle. A sensor unit comprising an RFID sensor for transmitting information is built in, and each tire house performs wireless communication with the RFID sensor of the sensor unit, and converts the ID information and resistance value of the RFID sensor into a voltage signal from a response signal. A reader for reading the measurement data consisting of the scaled data is arranged, an arithmetic control device for measuring the distortion of each tire by processing the measurement data obtained from each reader and driving the tire distortion information A tire distortion measuring system using an RFID sensor, characterized by comprising a monitor for informing a person .   As a driving power source for RFID sensors and magnetic sensors, a circuit power source that rectifies and stabilizes an induced electromotive force generated in an antenna by an electromagnetic field or electromagnetic wave output from a reader, and the circuit power source is stored in a large-capacity charging capacitor The tire strain measurement system using an RFID sensor according to claim 1, wherein the measured power is used.   3. The tire strain measuring system using an RFID sensor according to claim 1, wherein the magnetic sensor is a magnetoresistive element.   The brake control signal based on the change in tire distortion data is automatically transmitted to the brake braking device, and the brake control can be automatically performed. The engine control signal based on the change in tire distortion data is automatically transmitted to the engine control device. 2. The tire strain measuring system using an RFID sensor according to claim 1, wherein the engine can be controlled.

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