JP2007237781A - Tire air pressure monitoring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive tire air pressure monitoring system easy to mount. <P>SOLUTION: This system is provided with sensor units 3A to 3D provided in each of tires 2A to 2D to measure at least tire air pressure, radio terminals 4A to 4D provided corresponding to positions of the sensor units 3A to 3D to perform radio communication with each of the corresponding sensor units 3A to 3D, and a monitoring unit 5 for transmitting a command signal to instruct the sensor units 3A to 3D to transmit measuring signals including measured values of tire air pressure via the radio terminals 4A to 4D and monitoring tire air pressure based on the measuring signals received from the sensor units 3A to 3D via the radio terminals 4A to 4D. The system is provided with a battery line 10 connected to the monitoring unit 5 and the radio terminals 4A to 4D and battery line communication means (a communication equipment master station 8 and a battery line communication circuit 25) for making the monitoring unit 5 communicate with the radio terminals 4A to 4D via the battery line 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a tire pressure monitoring system for monitoring tire pressure in a vehicle.

  Conventionally, various systems for monitoring tire air pressure in a vehicle have been proposed. As an example, a sensor unit provided in each tire for measuring tire air pressure, a transmission coil antenna provided for each sensor unit for wireless communication with the corresponding sensor unit, and a transmission coil antenna. A monitoring unit that transmits a command signal (trigger signal) instructing transmission of a measurement signal (a signal including a measured value of tire air pressure) to the sensor unit, and that monitors tire air pressure based on the measurement signal received from the sensor unit. The provided structure is disclosed (for example, patent document 1). In the tire pressure monitoring system, trigger signals are transmitted as different code signals to the sensor unit with a predetermined time interval. The sensor unit transmits a measurement signal including the received code signal to the monitoring unit. As a result, the monitoring unit determines whether the measured value of the tire air pressure included in the measurement signal is equal to or less than a predetermined value while determining the position of the sensor unit that transmitted the measurement signal, and displays the determination result on the monitor. And give warnings.

JP 2004-161245 A

  In recent years, tire pressure monitoring systems have become mandatory in other countries such as North America, and demand is increasing in Japan as well. However, in the conventional tire pressure monitoring system, a dedicated communication line for connecting the monitoring unit inside the vehicle and a plurality of wireless terminals outside the vehicle has to be laid, and is particularly applicable to existing vehicles. In such a case, it is necessary to make a hole in the lower chassis of the vehicle body, and to perform waterproofing after passing a communication line through the hole. For this reason, it takes time and labor for laying, and the cost is high. In addition, instead of a dedicated communication line, for example, a method of wirelessly communicating a monitoring unit and a plurality of sensor units is also conceivable, but in this case, communication radio waves may be blocked by a metal chassis, The transmission power needs to be increased. For this reason, there is a possibility of affecting surrounding communication devices and electronic devices.

  An object of the present invention is to provide a tire pressure monitoring system that is inexpensive and easy to equip.

  (1) In order to achieve the above object, the present invention is provided in each of a plurality of tires, and is provided corresponding to at least a plurality of sensor units for measuring tire air pressure and the positions of the plurality of sensor units. A plurality of wireless terminals for wireless communication with each of the sensor units, and a command signal for instructing the plurality of sensor units to transmit a measurement signal including the measured value of the tire pressure via the plurality of wireless terminals. And a monitoring unit that monitors the tire pressure based on measurement signals received from the plurality of sensor units via the plurality of wireless terminals, and connected to the monitoring unit and the plurality of wireless terminals And the monitoring unit and the plurality of wireless terminals are passed through the battery line. And a battery line communication means for.

  In the present invention, there is provided battery line communication means for connecting the monitoring unit and the plurality of wireless terminals via a battery line, and for communicating the monitoring unit and the plurality of wireless terminals via the battery line. Thereby, a monitoring unit and a some radio | wireless terminal can be communicated via a battery line, and it becomes unnecessary to provide a dedicated communication line. In addition, the battery line can be connected to a monitoring unit inside the vehicle using, for example, a battery line that supplies electric power from a battery in the engine room to an electronic device inside the vehicle. It is possible to connect to a plurality of wireless terminals by pulling them through the openings. Thereby, compared with the case of laying a dedicated communication line or the like, it is not necessary to perform drilling or waterproofing of the chassis, and the labor of laying work can be reduced. Therefore, a tire pressure monitoring system that is inexpensive and easy to equip can be realized.

  (2) In the above (1), preferably, the battery line communication means allocates data to a carrier wave in a frequency range of 10 kHz to 450 kHz or 1.7 MHz to 30 MHz and performs communication.

  (3) In the above (2), preferably, the battery line communication means allocates data to a plurality of different carrier waves for communication.

  (4) In the above (2) or (3), preferably, the battery line communication means evaluates a signal-to-noise ratio S / N in the carrier wave, and the carrier wave according to the S / N evaluation. The data allocation amount setting means for changing the data allocation amount is provided.

  (5) In the above (2) or (3), preferably, the battery line communication means evaluates a transmission error rate in the carrier wave and changes the data allocation amount of the carrier wave according to the evaluation of the transmission error rate. And a data allocation amount setting means.

  (6) In the above (2), preferably, the battery line communication means performs communication by spreading the spectrum of a carrier to which data is allocated to a carrier having a wider bandwidth.

  (7) In any one of the above (1) to (6), the plurality of sensor units measure the tire air pressure, the tire air temperature, and the battery voltage built in the unit, respectively, and include the measured values. The monitoring unit transmits a signal and calculates and monitors a range of fluctuation of the tire pressure based on the measured value of the tire pressure of the tire air temperature, and monitors the battery life based on the measured value of the battery voltage.

  According to the present invention, it is possible to realize a tire pressure monitoring system that is inexpensive and easy to equip.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a schematic diagram showing the overall configuration of an embodiment of a tire pressure monitoring system of the present invention.

  In FIG. 1, this tire pressure monitoring system is applied to an automobile (four-wheeled passenger car) 1 and is provided on each of tires 2A to 2D, and measures tire pressure, tire air temperature, and unit built-in battery voltage. Wireless terminals 4A provided for sensor units 3A to 3D and the positions of these sensor units 3A to 3D (in other words, the positions of tires 2A to 2D) and wirelessly communicating with the corresponding sensor units 3A to 3D, respectively. To 4D and a command signal for instructing the sensor units 3A to 3D to transmit measurement signals including measured values (tire pressure, tire air temperature, and battery voltage) via the wireless terminals 4A to 4D, and a wireless terminal Tire pressure and battery voltage based on measurement signals received from sensor units 3A-3D via 4A-4D And a monitoring unit 5 to be monitored. Note that the monitoring unit 5 is disposed inside the vehicle.

  The wireless terminals 4A to 4D are installed, for example, on an axle housing, a steering knuckle, or a suspension arm, and the wireless communication distance with the corresponding sensor units 3A to 3D is relatively short. As a result, the energy of the radio signal (radio wave) can be reduced and the propagation range can be limited. Accordingly, the wireless terminals 4A to 4D can perform wireless communication only with the corresponding sensor units 3A to 3D.

  The monitoring unit 5 generates and outputs command signals to the sensor units 3A to 3D, and controls the tire pressure and battery voltage based on the measurement signals from the sensor units 3A to 3D. And a display device 7 for displaying a screen in response to an output signal from the control device 6. The control contents of the monitoring function of the control device 6 will be described with reference to FIG.

  FIG. 2 is a flowchart showing the contents of the control procedure of the control device 6.

  In FIG. 2, first, at step 100, the control device 6 outputs a command signal to the sensor units 3A to 3D. Thereby, the command signal is transmitted to the sensor units 3A to 3D via the wireless terminals 4A to 4D and the measurement signals are transmitted from the sensor units 3A to 3D accordingly. And it progresses to step 110 and the control apparatus 6 inputs the measurement signal from sensor unit 3A-3D via radio | wireless terminal 4A-4D etc. FIG. Note that the command signal and the measurement signal include address information of the wireless terminals 4A to 4D, respectively.

  Thereafter, the process proceeds to step 120, where the control device 6 calculates a tire air pressure variation range based on the tire air temperature and tire pressure included in the measurement signal, and proceeds to step 130, where the calculated tire air pressure variation range is calculated. It is determined whether it is below a predetermined value. For example, if the fluctuation range of the tire air pressure exceeds a predetermined value, the determination at step 130 is not satisfied, and the routine proceeds to step 150 described later. On the other hand, for example, if the fluctuation range of the tire air pressure is equal to or less than a predetermined value, the determination in step 130 is satisfied, and the routine proceeds to step 140. In step 140, a pneumatic alarm signal including address information of the corresponding wireless terminal (any one of 4A to 4D) is output to the display device 7.

  The display device 7 displays the screen shown in FIG. This screen shows the tire lighting parts (FL (front wheel left side), FR (front wheel right side), RL (rear wheel left side), RR (rear wheel right side) shown in FIG. 3 arranged to represent the positions of the tires 2A to 2D. ) And an air pressure display unit (XX1bar, XX2bar, XX3bar, XX4bar shown in FIG. 3) for displaying the air pressure measurement values of the tires 2A to 2D input from the control device 6. And according to the air pressure alarm signal from the control apparatus 6, the display apparatus 7 lights the tire lighting part corresponding to the address information of the radio | wireless terminal (any of 4A-4D) contained in the air pressure alarm signal. It is like that. As a result, the driver is notified of an abnormality in the tire air pressure.

  In step 150, it is determined whether or not the battery voltage included in the measurement signals from the sensor units 3A to 3D is equal to or lower than a predetermined value. For example, if the battery voltage exceeds a predetermined value, the determination in step 150 is not satisfied and the process ends. On the other hand, for example, when the battery voltage is equal to or lower than the predetermined value, the determination in step 150 is satisfied, and the process proceeds to step 160. In step 160, the control device 6 outputs a voltage alarm signal including the address information of the corresponding wireless terminal (any one of 4 </ b> A to 4 </ b> D) to the display device 7. The display device 7 blinks the tire lighting part corresponding to the address information of the wireless terminal (any one of 4A to 4D) included in the voltage warning signal. Accordingly, the driver is notified of the replacement time of the built-in batteries of the sensor units 3A to 3D, and measurement errors associated with a decrease in battery voltage are prevented.

  Here, as a major feature of the present embodiment, the monitoring unit 5 includes a communication device master station 8 connected to the control device 6 as shown in FIG. 1 described above. It is connected to a battery wire 10 connected to a battery 9 in the engine room. The wireless terminals 4A to 4D are also connected to the battery line 10, and communication is performed between the communication device master station 8 of the monitoring unit 5 and the wireless terminals 4A to 4D via the battery line 10. Details of the communication configuration of such a tire pressure monitoring system will be described with reference to FIGS.

  FIG. 4 is a block diagram showing the configuration of the communication device master station 8.

  In FIG. 4, the communication device master station 8 includes a protocol converter 11 that is an interface with the control device 6 (for example, a standard or a dedicated interface such as Ethernet or USB) and an access connected to the protocol converter 11. A controller 12, a coupler 13 connected to the battery line 10, and a transmission system 14 and a reception system 15 connected between the access controller 12 and the coupler 13 are provided. The coupler 13 is composed of a DC cut capacitor 13a and a high frequency transformer 13b that couples a communication signal (high frequency signal), and a DC voltage supplied from the battery 9 is generated inside the communication device master station 8. It is not applied.

The transmission system 14 includes a modulator 16, a digital / analog converter (D / A) 17, a transmission amplifier 18, in the order from the access controller 12 to the coupler 13.
A band-pass filter (BP filter) 19a is connected and configured. The reception system 15 includes a band-pass filter (BP filter) 19b, a reception amplifier 20, an analog / digital converter (A / D) 21, an equalizer 22, and a demodulator in the order from the coupler 13 to the access controller 12. 23 is connected. Further, the access controller 12 outputs a first data allocation amount table (data allocation amount of each carrier wave, in other words, a modulation scheme of each carrier wave, details will be described later) to the modulator 16, and the second data allocation amount table is displayed. The data is output to the demodulator 23.

  When the command signal from the control device 6 is input to the protocol converter 11, the protocol converter 11 sends a predetermined format (for example, as shown in FIG. 5, a preample signal 24a, a header 24b, data 24c, CRC ( (Cyclic Redundancy Check) 24d) and converted to a communication packet and output to the access controller 12. The access controller 12 creates packet data in which the address information of the wireless terminals 4A to 4D is included in the header 24b, and outputs the data to the modulator 16. The modulator 16 allocates data to the carrier wave (also referred to as bit allocation) based on the first data allocation amount table and outputs the signal. The digital signal output from the modulator 16 is converted into an analog signal by the D / A 17, amplified by the transmission amplifier 18, and output to the battery line 10 via the BP filter 19 a and the coupler 13.

  On the other hand, the measurement signal received from the battery line 10 via the coupler 13 is suppressed by the BP filter 19b, and the signal other than the communication band is suppressed, amplified by the reception amplifier 20, converted into a digital signal by the A / D 21, and equalized. Is output to the device 22. The equalizer 22 is for correcting the communication path distortion (also referred to as transmission path distortion) of the battery line 10, evaluates the communication path distortion of the battery line 10 using the preamble signal 24 a, and evaluates the evaluation. The signal is corrected (amplified) based on the above and output to the demodulator 23. The demodulator 23 extracts the data allocated to the carrier based on the second data allocation amount table and outputs the data to the access controller 12. The access controller 12 converts the packet data into a predetermined format based on the data from the demodulator 23 and outputs the packet data to the protocol converter 11. The protocol converter 11 converts the communication packet from the access controller 12 and outputs it to the control device 6.

  The communication device master station 8 may sequentially access the wireless terminals 4A to 4D, for example, by a polling method.

  FIG. 6 is a block diagram showing the configuration of the wireless terminal 4A (or 4B, 4C, 4D).

  In FIG. 6, a wireless terminal 4A (or 4B, 4C, 4D) is connected to the battery line communication circuit 25 connected to the battery line 10 and to the corresponding sensor unit 3A (or to the battery line communication circuit 25). 3B, 3C, 3D) and a wireless communication circuit 26 and an antenna 27 for wireless communication. The battery line communication circuit 25 has substantially the same configuration as that of the communication device master station 8, and detailed illustration and description of the configuration are omitted.

  The wireless communication circuit 26 includes an access controller 28 connected to the battery line communication circuit 25, and a transmission system 29 and a reception system 30 connected between the access controller 28 and the antenna 27. In the transmission system 29, a modulator 31, a digital / analog converter (D / A) 32, a mixer 33a, a transmission amplifier 34, and a band pass filter (BP filter) 35a are connected in the order from the access controller 28 to the antenna 27. It is configured. The reception system 30 includes, in order from the antenna 27 to the access controller 28, a bandpass filter (BP filter) 35b, a reception amplifier 36, a mixer 33b, a bandpass filter (BP filter) 37, and an analog / digital converter (A / D). 38), an equalizer 39, and a demodulator 40 are connected to each other. In addition, the access controller 28 outputs a third data allocation amount table to the modulator 31 and outputs a fourth data allocation amount table to the demodulator 40.

  When the command signal from the battery line 10 is received by the battery line communication circuit 25, the communication packet converted by the battery line communication circuit 25 through a predetermined procedure is output to the access controller 28, and the data is modulated. Is output to the device 31. The modulator 31 allocates data to the carrier based on the third data allocation amount table and outputs the signal. The digital signal output from the modulator 31 is converted into an analog signal by the D / A 32, converted into a signal in the wireless communication band by the mixer 33a (specifically, shifted by the frequency from the transmitter 41), and a transmission amplifier 34, and is transmitted from the antenna 27 through the BP filter 35a.

  On the other hand, in the measurement signal received from the antenna 27, a signal other than the radio communication band is suppressed by the BP filter 35b, amplified by the reception amplifier 36, and returned to the baseband signal by the mixer 33b. 41 is shifted by the frequency of the signal from 41). Then, the BP filter 37 removes the secondary wave (such as a beat wave generated when converting to the baseband), converts it into a digital signal by the A / D 38, and the equalizer 39 performs channel distortion (transmission path) of the wireless communication. (Also referred to as distortion) is corrected and output to the demodulator 40. The demodulator 40 extracts the data allocated to the carrier wave based on the fourth data allocation amount table and outputs the data to the access controller 28. The access controller 28 converts the data from the demodulator 40 into a communication packet of a predetermined format and outputs it to the battery line communication circuit 25.

  FIG. 7 is a block diagram showing the configuration of the sensor unit 3A (or 3B, 3C, 3D).

  In FIG. 7, the sensor unit 3A (or 3B, 3C, 3D, and the same corresponding to the parenthesis in the following) includes the air pressure sensor 42 that measures the air pressure of the tire 2A (or 2B, 2C, 2D), and the tire 2A (or 2B, 2C, 2D), an air temperature sensor 43 for measuring the air temperature, a battery voltage sensor 44 for measuring the voltage of a battery (not shown) built in the sensor unit 3A, the air pressure sensor 42, the air temperature sensor 43, And a control circuit 45 that receives measurement values from the battery voltage sensor 44 and generates a measurement signal including these measurement values, and a wireless communication circuit for wirelessly communicating with the corresponding wireless terminal 4A (or 4B, 4C, 4D) 46 and an antenna 47, and a protocol converter 48 provided between the control circuit 45 and the wireless communication circuit 46. The wireless communication circuit 46 has substantially the same configuration as the wireless communication circuit 26 of the wireless terminal 4A (or 4B, 4C, 4D), and detailed illustration and description of the configuration will be omitted.

  When the command signal is received by the wireless communication circuit 46 via the antenna 47, the communication packet converted by the wireless communication circuit 46 through a predetermined procedure is output to the control circuit 45 via the protocol converter 48. In response to this, the control circuit 45 includes the address information of the wireless terminal 4A (or 4B, 4C, 4D) in the header 24b (see FIG. 5 described above), and the tire air pressure, tire air temperature, and battery voltage. The packet data including the measurement value in the data 24c (see FIG. 5 described above) is created, and the packet data is output to the wireless communication circuit 46 via the protocol converter 48. A signal (measurement signal) converted through a predetermined procedure in the wireless communication circuit 46 is transmitted from the antenna 47.

  Next, details of the characteristics of communication via the battery line 10 between the above-described communication device master station 8 and the wireless terminals 4A to 4D will be described.

  In general, the noise superimposed on the battery line 10 becomes higher as the frequency becomes lower. Therefore, the frequency of the carrier wave is preferably 10 kHz or more. Further, since the battery line 10 has frequency-dependent characteristics, and the signal attenuation amount increases and fluctuates as the frequency becomes higher, the frequency of the carrier wave is desirably 30 MHz or less. Note that the signal attenuation in the battery line 10 is due to the inductance of the battery line 10, the attenuation due to the electrostatic capacity between the forward path and the return path, reflection at the end point of the battery line 10, and the like. Therefore, in order to stabilize the communication via the battery line 10, it is necessary to suppress the signal attenuation while maintaining the signal / noise ratio S / N (which is a difference in dB) above a predetermined value. It is desirable to use within a frequency band of 10 kHz to 30 MHz. In general, a radio is provided in the vehicle 1, and it is desirable to avoid an influence on communication in the AM band (a range of about 500 kHz to 1.6 MHz). Therefore, in the present embodiment, the communication via the battery line 10 assigns data to a carrier wave within a frequency range of 10 kHz to 450 kHz or 1.7 MHz to 30 MHz.

  Further, as can be seen from the measurement results of the inventors of the present invention shown in FIGS. 8 and 9, the battery line 10 varies in noise level according to the operation state of the automobile 1 (for example, the operation state of the engine, the air conditioner, etc.). To do. More specifically, for example, the noise voltage is as low as several dBμV or less in a frequency band of 30 MHz or less when the engine is stopped, whereas for example, a specific frequency band (approximately 0.3 MHz or less in FIG. 8) during engine operation. In the range of about 4 to 6 MHz and about 15 to 16 MHz), the noise voltage is 10 dBμV or more. Further, for example, in a frequency band of 30 MHz or less during the operation of the air conditioner, the noise voltage is in a range of about 10 to 45 dBμV and is relatively large.

  Therefore, in the present embodiment, in order to perform communication efficiently in accordance with the operation state of the automobile 1, the S / N of the carrier wave is evaluated (estimated) as the communication characteristic of the battery line 10 at regular time intervals (for example, 1 second). Alternatively, control is performed to set the data allocation amount of the carrier according to the S / N evaluation. That is, a first data allocation amount table (similarly, an access controller (not shown) in the battery line communication circuit 25 of the wireless terminals 4A to 4D) output from the access controller 12 to the modulator 16 in the communication device master station 8 described above. From the access controller 12 in the communication device master station 8 to the demodulator 23 (similarly, the wireless terminal 4A). The second data allocation amount table output from the access controller to the modulator (not shown) in the 4D battery line communication circuit 25 is not always constant and is changed according to the S / N evaluation. Yes.

  More specifically, the access controller 12 of the communication device master station 8 or the access controller of the battery line communication circuit 25 of the wireless terminals 4A to 4D is based on communication error characteristics as shown in FIG. And modulation schemes (256QAM, 128QAM (not shown), 64QAM, 32QAM (not shown), 16QAM, QPSK, BPSK, etc. in FIG. 10) are set according to the setting value (fixed value) of the transmission error rate. Is used to set the data allocation amount (bit allocation amount) of the carrier wave. That is, 8 bits for 256QAM, 6 bits for 64QAM, 4 bits for 16QAM, 2 bits for QPSK, and 1 bit for BPSK can be allocated. According to the communication error characteristics of FIG. 10, for example, when the transmission error rate is set to 1E-5, 256QAM (Quadrature Amplitude Modulation), 64QAM, 16QAM, QPSK (Quadrature Phase Shift Keying) , BPSK (Binary Phase Shift Keying) modulation methods must have S / N of about 22.5 dB, about 17.7 dB, about 13.5 dB, about 9.5 dB, and about 6.3 dB, respectively. I must.

  There are two types of communication methods via the battery line 10: a multi-carrier method in which data is assigned to a plurality of carrier waves and a single carrier method in which data is assigned to a single carrier wave for communication. In the form, a multi-carrier system is adopted. In the general multicarrier scheme, as shown in FIG. 11, a plurality of carriers are allocated to the use band ΔF1 by taking a predetermined band space between the carriers so that a plurality of carriers having the bandwidth Δf do not overlap. ing. By adopting such a multi-carrier system, it is possible to ensure a high transmission rate. That is, for example, when the noise level of a specific frequency is high, the data allocation amount of the carrier wave that matches the noise frequency is reduced, but by using a plurality of carrier waves, the decrease in the data allocation amount as a whole is suppressed, It is possible to ensure a high transmission rate. In addition, as shown in FIG. 12, an ODFM (Orthogonal Frequency Division Multiplexing) method, which is a kind of multi-carrier method, causes a power peak point of one carrier to overlap with a power zero point of another carrier. And maintaining orthogonality by inverse Fourier transform at time 1 / (Δf / 2). This ODFM method has higher frequency band utilization efficiency than the general multi-carrier method, and can narrow the use band ΔF2.

  Next, the procedure of the above-described setting control of the data allocation amount of the carrier wave will be described. FIG. 13 is a flowchart for explaining the procedure of setting control of the first data allocation amount table.

  In FIG. 13, first, normal processing of the access controller 12 of the communication device master station 8 in response to a command signal from the control device 6 will be described. In step 200, the access controller 12 includes information (code) indicating normal data in the header 24b based on the data fetched from the protocol converter 11, and further adds address information of the radio terminals 4A to 4D. Each included packet data is created, and the data is output to the modulator 16. As a result, the data modulated by the modulator 16 is transmitted to the corresponding wireless terminals 4A to 4D via the battery line 10. Then, measurement signals from the wireless terminals 4A to 4D are received by the communication device master station 8 via the battery line 10, and the data allocated to the carrier wave is extracted by the demodulator 23. In step 210, the access controller 12 takes in the data from the demodulator 23, proceeds to step 220, evaluates the CRC 24d (see FIG. 5 described above), and determines whether there is a transmission error. Thereafter, the process proceeds to step 230. For example, when there is a transmission error, a retransmission request is made to the corresponding wireless terminals 4A to 4D via the battery line 10, and when there is no transmission error, a predetermined format is set based on the captured data. Packet data is created and output to the protocol converter 11.

  Then, the access controller 12 of the communication device master station 8 performs an interrupt process for S / N evaluation of each carrier wave at regular intervals while performing the above-described normal process. In step 300, the access controller 12 first prepares training data (specifically, the header 24b includes information indicating that it is training data, and the data 24c includes training data. Packet data including address information of the wireless terminals 4A to 4D in the header 24b) is output to the modulator 16. Thus, the training data is modulated by the modulator 16 (assigned to each carrier wave) and transmitted to the corresponding wireless terminals 4A to 4D via the battery line 10. In this case as well, the wireless terminals 4A to 4D may be sequentially accessed by, for example, a polling method.

  Then, proceeding to step 400, the access controller of the battery line communication circuit 25 of the wireless terminals 4A to 4D takes in training data received from the carrier wave and received from the carrier by the demodulator. Then, it progresses to step 410 and evaluates S / N of each carrier wave.

  The details of the S / N evaluation method for each carrier wave will be described by taking, for example, a case of using a QPSK modulation method in which 2 bits are assigned to each carrier wave. FIG. 14 is a diagram illustrating the signal point arrangement of QPSK, where the vertical axis (I axis) represents the in-phase component of the signal, and the horizontal axis (Q axis) represents the quadrature component of the signal. As shown in FIG. 14, the data assignment to the signal points is as follows: the signal point in the first quadrant is data “00”, the signal point in the second quadrant is data “01”, and the signal point in the third quadrant is data. The signal point in the fourth quadrant indicates “11” and data “10”. In this embodiment, in order to evaluate the S / N more accurately, all the data “00”, “01”, “11”, and “10” are used as training data. Also, a first data allocation amount table output from the access controller 12 of the communication device master station 8 to the modulator 16 (similarly, output from the access controller of the battery line communication circuit 25 of the wireless terminals 4A to 4D to the demodulator. The first data allocation amount table) is set so that 2 bits are allocated to each carrier wave (in other words, the modulation scheme of QPSK).

  And the access controller of the battery line communication circuit 25 of radio | wireless terminal 4A-4D evaluates S / N by a method as shown in FIG. More specifically, if there is no noise and no attenuation on the communication channel, the demodulated signal points are true values (“00”, “01”, “11”, “10”). However, there is noise and attenuation on the communication path. Since attenuation is corrected (amplified) by the equalizer, the demodulated signal including noise is restored around the true value. The distance from the origin to the true value in FIG. 15 is the signal strength S, and the distance from the true value to the demodulated signal point position is the noise intensity N. If the ratio between these two is calculated, S / N is required. Instead of calculating S / N using a true value, an average value of demodulated signal point positions may be calculated, and S / N may be calculated using this average value.

  Returning to FIG. 13, the process proceeds to step 420, where the access controller of the battery line communication circuit 25 of the wireless terminals 4 </ b> A to 4 </ b> D evaluates S / N (and transmission) of each carrier based on the characteristic relationship shown in FIG. 10. The data allocation amount of each carrier wave is set according to the error rate setting value), thereby rewriting the first data allocation amount table. Thereafter, the process proceeds to step 430, where the access controller includes packet data in a predetermined format based on the updated data allocation amount of each carrier (for example, information including a combination of a carrier number and a data allocation amount is included in the data 24c, and the wireless terminal 4A ~ 4D address information is included in the header 24b) and output to the modulator. Thereby, the signal modulated by the modulator is transmitted to the communication device master station 8 via the battery line 10.

  Then, signals from the wireless terminals 4 </ b> A to 4 </ b> D are received via the battery line 10, and data allocated to the carrier wave is extracted by the demodulator 23. In step 310, the access controller 12 takes in data from the demodulator 23, proceeds to step 320, and rewrites the first data allocation amount table. Thereafter, the process proceeds to step 330, and the access controller 12 of the communication device master station 8 transmits ACK (confirmation signal) to the wireless terminals 4A to 4D. Then, the process proceeds to step 440, where the access controller of the battery line communication circuit 25 of the wireless terminals 4A to 4D receives ACK and ends the setting control of the first data allocation amount table.

  For example, the communication characteristics of the battery line 10 are not symmetric (in other words, the transmission characteristics from the communication device master station 8 to the radio terminals 4A to 4D and the transmission characteristics from the radio terminals 4A to 4D to the communication device master station 8 are symmetric). If not, the setting control of the second data allocation amount table is started after the end of the setting control of the first data allocation amount table. The access controller of the battery line communication circuit 25 of the wireless terminals 4A to 4D transmits training data, and the access controller 12 of the communication device master station 8 evaluates the S / N of each carrier in response to this, and this S / N Based on the evaluation, the data allocation amount of each carrier wave is set, whereby the second data allocation amount table in the access controller 12 of the communication device master station 8 and the access controller of the battery line communication circuit 25 of the wireless terminals 4A to 4D is obtained. Rewritten. On the other hand, for example, when the communication characteristics of the battery line 10 can be regarded as symmetric, the second data allocation amount table can be rewritten as the same as the first data allocation amount table.

  In the above, the communication device master station 8 of the monitoring unit 5 and the battery line communication circuit 25 of the wireless terminals 4A to 4D are batteries that allow the monitoring unit to communicate with a plurality of wireless terminals via the battery line described in the claims. The line communication means is configured. The access controller 12 of the communication device master station 8 and the access controller of the battery line communication circuit 25 evaluate the signal / noise ratio S / N in the carrier wave, and assign the carrier data according to the S / N evaluation. A data allocation amount setting means for changing the amount is configured.

  In the present embodiment configured as described above, the communication device master station 8 of the monitoring unit 5 and the battery line communication circuit 25 of the wireless terminals 4A to 4D are connected by the battery line 10, and communication is performed via the battery line 10. Let This eliminates the need to provide a dedicated communication line. In addition, the battery line 10 can be connected to the monitoring unit 5 on the vehicle interior, for example, using a battery wire that supplies power from the battery 9 in the engine room to the electronic device on the vehicle interior. In addition, since the engine room usually does not have a sealed structure, it can be easily routed through the battery line 10 to the opening on the lower side and connected to the wireless terminals 4A to 4D. Further, for example, in a vehicle in which an electric brake is provided in a tire portion such as Break-by-Wire, which is being studied in the future, the wireless terminals 4A to 4A using a battery line that supplies electric power from the battery 9 to the electric brake. It is possible to connect with 4D. Thus, in this embodiment, compared with the case where a dedicated communication line or the like is laid, there is no need to perform drilling or waterproofing of the chassis, and the labor and cost of laying work can be reduced. Therefore, a tire pressure monitoring system that is inexpensive and easy to equip can be realized.

  Further, in the present embodiment, the monitoring unit 5 transmits the command signal to the sensor units 3A to 3D by designating the addresses of the wireless terminals 4A to 4D, and detects the measurement signal including the address information of the wireless terminals 4A to 4D. Receive from units 3A-3D. Thereby, the monitoring unit 5 can identify whether the measurement signals from the sensor units 3A to 3D are transmitted from any of the wireless terminals 4A to 4D, and the positions of the wireless terminals 4A to 4D, that is, the tires 2A to 2A. The tire pressure corresponding to the 2D position can be monitored. Therefore, it is possible to cope with the case where rotation of the tires 2A to 2D occurs.

  In the present embodiment, the access controller 12 of the communication device master station 8 and the access controller of the battery line communication circuit 25 dynamically evaluate the communication characteristics (signal / noise ratio S / N) of the battery line 10, Based on the evaluation, the data allocation amount of each carrier wave is changed. Thereby, it is possible to communicate efficiently while suppressing the occurrence of transmission errors.

  In the above-described embodiment, the case where the training data is transmitted at regular time intervals to evaluate the S / N of the carrier wave has been described as an example. However, the present invention is not limited to this. That is, for example, training data may be transmitted for each event to evaluate the S / N of the carrier wave. Such a modification will be described with reference to FIG.

  FIG. 16 is a flowchart showing the procedure contents of the setting control of the first data allocation amount table according to this modification. In FIG. 16, the same steps as those in FIG. 13 are given the same reference numerals.

  In this modification, in Step 240, the access controller 12 of the communication device master station 8 calculates a transmission error rate at regular intervals. In step 250, it is determined whether the transmission error rate is equal to or higher than a predetermined value. If the transmission error rate is less than the predetermined value, the process ends. On the other hand, if the transmission error rate is greater than or equal to the predetermined value, the process proceeds to step 300 described above, and training data is output to the modulator 16. In such a modification, the S / N is evaluated when the transmission error rate exceeds a predetermined value, and the data allocation amount of the carrier wave is set according to the S / N evaluation. More can be prevented. For example, when the training data is transmitted at regular time intervals and every event and the S / N is evaluated, the effects of preventing the occurrence of transmission errors and improving the transmission efficiency can be further obtained.

  In the above embodiment, the modulation scheme is set according to the S / N evaluation (variation value) and the set value (fixed value) of the transmission error rate based on the communication error characteristics as shown in FIG. In this example, the case where the data allocation amount of the carrier wave is set has been described as an example, but the present invention is not limited to this. That is, for example, the transmission error rate may be evaluated, and the data allocation amount of the carrier wave may be set according to the evaluation (variation value) of the transmission error rate and the set value (fixed value) of S / N. Further, for example, the S / N and the transmission error rate may be evaluated, and the data allocation amount of the carrier wave may be set according to the evaluation (variation value) of the transmission error rate and the evaluation (variation value) of the S / N. In these cases, the same effect as in the above embodiment can be obtained.

  For example, instead of setting the data allocation amount of the carrier wave, a change amount (shift amount) of the frequency of the carrier wave may be set. In such a modification, the access controller of the communication device master station and the access controller of the battery line communication circuit of the wireless terminal output the carrier frequency change amount to the modulator and demodulator instead of the data allocation amount table. The modulator and demodulator change the frequency of the carrier wave to a frequency with a low noise level based on the frequency change amount. Also in such a modification, the same effect as the above-described embodiment can be obtained.

  Further, in the above-described embodiment, the communication via the battery line 10 has been described by taking as an example the case of employing a multi-carrier method in which communication is performed using a plurality of carrier waves. May be adopted. However, in order to realize the same transmission rate as that of the multicarrier system, it is necessary to widen the bandwidth of the carrier wave.

  Further, for example, a spread spectrum communication method may be employed in which a carrier to which data is allocated is spread to a carrier having a wider bandwidth for communication. FIG. 17 is a block diagram showing the configuration of the communication device master station in such a modification. Note that, in FIG. 17, parts that are the same as in the above embodiment are given the same reference numerals, and descriptions thereof are omitted as appropriate.

  In the present modification, a spread spectrum modulator 49 is connected between the modulator 16 (primary modulator) and the D / A 17 in the communication device master station 8 ′. The spread spectrum modulator 49 multiplies the signal from the modulator 16 (the signal first modulated by the modulator 16) with a special waveform called a PN (Pseudorandom Noise) sequence from the spread code generator 50. The signal is spread-modulated and output to the D / A 17. At this time, the bandwidth of the carrier wave modulated by the spread spectrum modulator 49 is the sum of the bandwidth of the primary modulation (baseband bandwidth) and the bandwidth of the PN sequence. If it is large, the bandwidth is substantially the PN sequence. Since the automobile 1 has a relatively high noise level, it is desirable that the magnification of the diffusion modulation is at least 10 times or more.

  A spread spectrum despreader 51 is connected between the A / D 21 and the demodulator 23, and a timing / synchronization circuit 52 for synchronization is connected to the spread spectrum despreader 51 and the A / D 21. Has been. The spread spectrum despreader 51 multiplies the signal from the A / D 21 by the PN sequence from the spread code generator 51 to restore (band compression) to the primary modulation bandwidth.

  Note that the spread spectrum modulator 49 can be realized by an analog processing circuit, in which case the D / A 17 is not necessary. Further, the spread spectrum despreader 51 and the timing / synchronization circuit 52 can be realized by an analog processing circuit, and in this case, the A / D 21 is not necessary. Note that the battery line communication circuit 25 ′ of the wireless terminals 4 </ b> A to 4 </ b> D has substantially the same configuration as the communication device master station 8 ′, and illustration and description thereof are omitted.

  Then, the signal spread-modulated by the spread spectrum modulator 49 of the communication device master station 8 ′ is transmitted via the battery line 10 and band-compressed by the spread spectrum despreader of the battery line communication circuit 25 ′ of the wireless terminals 4A to 4D. Is done. Further, the signal spread-modulated by the spread spectrum modulator of the battery line communication circuit 25 ′ of the wireless terminals 4A to 4D is transmitted via the battery line 10 and band-compressed by the spread spectrum despreader 51 of the communication device master station 8 ′. Is done. By such spread modulation and band compression, it is possible to suppress frequency-selective noise (see the above-mentioned figure) during engine operation and the like, and to avoid the influence of noise on the communication path. This eliminates the need to perform setting control (see the above-described figure) of the data allocation amount of the carrier wave in the one embodiment, and makes it possible to avoid a temporary communication interruption.

  Although not particularly described in the above embodiment, in communication via the battery line 10, the battery 9 connected to the battery line 10 behaves like a capacitor and absorbs a high-frequency communication signal. There is a possibility of lowering the signal level. In order to cope with this, for example, a choke coil 53 may be provided on the positive electrode side of the battery 9 as shown in FIG. Thereby, while not affecting the direct current output of the battery 9, it is possible to increase the impedance of the communication signal with respect to the high frequency, prevent the behavior of the capacitor by the battery 9, and suppress the attenuation of the communication signal. . Even in such a case, the same effect as the above-described embodiment can be obtained.

It is the schematic showing the whole structure of one Embodiment of the tire pressure monitoring system of this invention. It is a flowchart showing the control procedure content of the control apparatus of the monitoring unit which comprises one Embodiment of the tire pressure monitoring system of this invention. It is a figure showing the screen displayed on the display apparatus of the monitoring unit which comprises one Embodiment of the tire pressure monitoring system of this invention. It is a block diagram showing the structure of the communication apparatus main | base station which comprises one Embodiment of the tire pressure monitoring system of this invention. It is a figure showing the format of the packet data in one Embodiment of the tire pressure monitoring system of this invention as an example. It is a block diagram showing the structure of the radio | wireless terminal which comprises one Embodiment of the tire pressure monitoring system of this invention. It is a block diagram showing the structure of the sensor unit which comprises one Embodiment of the tire pressure monitoring system of this invention. It is a figure showing the measurement result of the noise of a battery line at the time of an engine stop and operation. It is a figure which shows the measurement result of the noise of a battery line at the time of air-conditioner operation | movement. It is a figure showing the communication error characteristic under Gaussian noise. It is a figure for demonstrating a general multicarrier system as an example of the communication system via the battery line in one Embodiment of the tire pressure monitoring system of this invention. It is a figure for demonstrating the ODFM system as another example of the communication system via the battery line in one Embodiment of the tire pressure monitoring system of this invention. It is a flowchart for demonstrating the procedure content of the setting control of the data allocation amount of the carrier wave in one Embodiment of the tire pressure monitoring system of this invention. It is a figure showing the signal point arrangement | positioning of QPSK. It is a figure for demonstrating S / N evaluation of QPSK. It is a flowchart for demonstrating the procedure content of the setting control of the data allocation amount table in the modification of the tire pressure monitoring system of this invention. It is a block diagram showing the structure of the communication apparatus main station which comprises the other modification of the tire pressure monitoring system of this invention. It is a figure showing the whole structure of the other modification of the tire pressure monitoring system of this invention.

Explanation of symbols

2A to 2D Tires 3A to 3D Sensor units 4A to 4D Wireless terminal 5 Monitoring unit 8 Communication device master station (battery line communication means)
10 battery line 12 access controller (data allocation amount setting means)
25 Battery line communication circuit (battery line communication means)

Claims (7)

A plurality of sensor units that are provided in each of the plurality of tires and measure at least tire air pressure, and a plurality of wireless terminals that are provided corresponding to the positions of the plurality of sensor units and wirelessly communicate with the corresponding sensor units. And a command signal instructing transmission of the measurement signal including the measured value of the tire air pressure to the plurality of sensor units via the plurality of wireless terminals, and from the plurality of sensor units via the plurality of wireless terminals. In a tire pressure monitoring system comprising a monitoring unit that monitors the tire pressure based on a received measurement signal,
A battery line connected to the monitoring unit and a plurality of wireless terminals;
A tire air pressure monitoring system comprising battery line communication means for communicating the monitoring unit and the plurality of wireless terminals via the battery line.   2. The tire pressure monitoring system according to claim 1, wherein the battery line communication means allocates data to a carrier wave in a frequency range of 10 kHz to 450 kHz or 1.7 MHz to 30 MHz and performs communication. system.   3. The tire pressure monitoring system according to claim 2, wherein the battery line communication means allocates data to a plurality of different carrier waves for communication.   The tire pressure monitoring system according to claim 2 or 3, wherein the battery line communication means evaluates a signal-to-noise ratio S / N in the carrier wave, and assigns the carrier data according to the S / N evaluation. A tire pressure monitoring system comprising a data allocation amount setting means for changing the amount.   The tire pressure monitoring system according to claim 2 or 3, wherein the battery line communication means evaluates a transmission error rate in the carrier wave and changes the data allocation amount of the carrier wave according to the evaluation of the transmission error rate. A tire pressure monitoring system comprising a quantity setting means.   3. The tire pressure monitoring system according to claim 2, wherein the battery line communication means spreads and communicates a carrier wave to which data is allocated to a carrier wave having a wider bandwidth.   The tire pressure monitoring system according to any one of claims 1 to 6, wherein the plurality of sensor units measure the tire pressure, the tire air temperature, and the battery voltage built in the unit, respectively, and include the measured values. The monitoring unit calculates and monitors the fluctuation range of the tire pressure based on the measured values of the tire air temperature and the tire pressure, and monitors the battery life based on the measured value of the battery voltage. Features tire pressure monitoring system.

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