JP5217738B2 - Tire pressure transmitter - Google Patents

Description

  The present invention relates to a tire pressure transmitter.

  2. Description of the Related Art Conventionally, a technique of a tire pressure transmitter that is mounted on a wheel, detects tire pressure of the wheel, and repeatedly transmits information on the detected tire pressure is known.

  This tire pressure transmitter is often required to operate normally even in a low temperature environment of about -40 ° C. However, in such a low-temperature environment, even if the battery provided in the tire pressure transmitter is a new battery, the voltage drops. If the voltage drops significantly, there is a high risk that the tire pressure transmitter will not operate normally.

  In view of such circumstances, Patent Document 1 proposes a technique for normally operating a tire pressure transmitter in a lower temperature environment. In the technique of Patent Document 1, the tire pressure transmitter has a temperature sensor that detects the ambient temperature, and based on the fact that the temperature detected by the temperature sensor has fallen below a predetermined threshold, The transmission frequency is reduced.

By doing in this way, the fall of the voltage of a battery can be suppressed under a low temperature environment, and a tire pressure transmitter can be normally operated under a lower temperature environment.
Japanese Patent Laid-Open No. 2001-14581

  However, in the technique disclosed in Patent Document 1, the temperature sensor needs to detect the temperature. Since the detection accuracy of the temperature sensor in a low temperature environment of about −40 ° C. is generally in the range of about ± 5 ° C., the temperature detection accuracy may be insufficient.

  In view of the above points, the present invention provides a technique for detecting a temperature environment in which the transmission frequency should be reduced without relying on a temperature sensor in a tire pressure transmitter that reduces the transmission frequency of tire pressure information in a low temperature environment. The purpose is to provide.

  The invention described in claim 1 for achieving the above object relates to a tire pressure transmitter that is mounted on a wheel, detects the tire pressure of the wheel, and repeatedly transmits information on the detected tire pressure.

  The tire pressure transmitter includes a battery (11) that supplies power for transmitting tire pressure information in the tire pressure transmitter, and a voltage of the battery (11) when the tire pressure information is being transmitted. , And a frequency reduction means (148) for reducing the transmission frequency of tire pressure information based on the fact that the voltage read by the reading means (144) has fallen below the reference voltage. ing.

  Thus, the tire pressure transmitter reads the voltage of the battery (11) when the tire pressure information is being transmitted, and the tire pressure information of the tire pressure information is triggered when the read voltage falls below the reference voltage. The transmission frequency is reduced.

  The voltage of the battery (11) when tire pressure information is transmitted is more sensitive to changes in ambient temperature than the voltage of the battery (11) when tire pressure information is not transmitted. Change.

  Therefore, by using the voltage of the battery (11) when the tire air pressure information is transmitted, it is possible to accurately detect that the temperature environment should be reduced without depending on the temperature sensor. .

Further, the reading means (144), at the end of one transmission period tire pressure, may be adapted to read the voltage of the battery (11). In one transmission period of the tire pressure, the voltage of the battery (11) continues to decrease, and when the transmission period ends, the voltage of the battery (11) recovers to some extent. Therefore, the voltage of the battery (11) is the lowest at the end of the transmission period.

  And as the voltage is lower, the voltage changes more sensitively to ambient temperature changes, so the end of the transmission period is a detection voltage for detecting that the temperature environment should reduce the transmission frequency. Is optimal.

  Further, the temperature environment in which the transmission frequency should be reduced is a temperature environment immediately before the voltage of the battery (11) starts to fall below the minimum operating voltage of the tire pressure transmitter, for detecting such an environment. As the voltage, the voltage in the lowest state is optimal.

According to a second aspect of the present invention, the tire pressure transmitter includes a storage medium (17c) for storing a reference voltage, and the frequency reduction means (148) reads the reference voltage from the storage medium (17c) and detects it. The transmission frequency of the tire air pressure information may be reduced based on the fact that the measured voltage is lower than the read reference voltage.

  In this way, the tire pressure transmitter stores the optimum reference voltage according to the characteristics of the tire pressure transmitter in advance, and compares the detected voltage with the reference voltage to control the transmission frequency based on the result. When creating the function to be performed as a program, it is not necessary to change the program for each characteristic of the tire pressure transmitter, and the program can be shared between tire pressure transmitters having different characteristics.

  In addition, the code | symbol in the bracket | parenthesis in the said and the claim shows the correspondence of the term described in the claim, and the concrete thing etc. which illustrate the said term described in embodiment mentioned later. .

  Hereinafter, embodiments of the present invention will be described. FIG. 1 shows a block configuration of a tire pressure monitoring system in the present embodiment. As shown in this figure, the tire pressure monitoring system is attached to a vehicle, and includes a tire pressure transmitter 1, a vehicle body side antenna 21, an ECU 22, and a display 3. The vehicle body side communication device is constituted by the vehicle body side antenna 21 and the ECU 22.

  As shown in FIG. 1, a plurality of tire pressure transmitters 1 are each attached to each wheel of a vehicle, and the corresponding tire internal air pressure (hereinafter referred to as tire air pressure), the corresponding tire internal temperature ( Hereinafter, the tire temperature is detected, and data such as the detected tire pressure and tire temperature is transmitted wirelessly.

  Each of the plurality of vehicle body side antennas 21 is attached in the vicinity of each wheel of the vehicle, receives a radio signal transmitted from the tire pressure transmitter 1 attached to each corresponding wheel, and outputs it to the ECU 22. To do.

  The ECU 22 receives the data in the signal transmitted from each tire pressure transmitter 1 via the vehicle body side antenna 21 and identifies the tire pressure and tire temperature of each wheel based on the received data. Information on tire pressure and tire temperature is displayed on the display 3.

  FIG. 2 shows a block configuration of each tire pressure transmitter 1. The tire pressure transmitter 1 includes a transmission antenna 10, a battery 11, and a sensor IC 12. The sensor IC 12 realizes a function of detecting the tire air pressure and the tire temperature of the tire to which the tire air pressure transmitter 1 is attached and performing an operation of transmitting the detected tire air pressure and tire temperature information using the transmission antenna 10. IC chip.

  The battery 11 is a battery that converts chemical energy into electrical energy, and serves as a power supply source for the operation of the sensor IC 12 by supplying power to the circuit of the sensor IC 12.

  Hereinafter, the internal configuration of the sensor IC 12 will be described. The sensor IC 12 includes an RF transmission unit 13, a voltage sensor 14, a pressure sensor 15, a temperature sensor 16, and a control unit 17.

  The RF transmission unit 13 performs predetermined modulation, frequency conversion, amplification, and the like on the data output from the control unit 17, and uses the transmission antenna 10 as a radio signal for a signal obtained as a result of the processing. Transmit to the side antenna 21.

  The voltage sensor 14 is a circuit that constantly detects a voltage applied by the battery 11 to the sensor IC 12 (more specifically, the control unit 17 and the RF transmission unit 13) and outputs the detected signal to the control unit 17. More specifically, the voltage sensor 14 can detect the voltage of the battery 11 by being connected to the battery 11 in parallel with the control unit 17 and the RF transmission unit 13.

  The pressure sensor 15 is a well-known pressure sensor (for example, a diaphragm type pressure sensor) that detects tire air pressure, and outputs a signal indicating the detected tire air pressure to the control unit 17. The temperature sensor 16 is a well-known temperature sensor that detects the tire temperature, and outputs a signal indicating the detected tire temperature to the control unit 17.

  The control unit 17 is a microcomputer including a CPU 17a, a RAM 17b, a ROM 17c, an I / O 17d, and the like. The CPU 17a performs processing for realizing various functions of the control unit 17 by reading the program recorded in the ROM 17c into the RAM 17b and executing it.

  In the process, the CPU 17a reads the signals output from the voltage sensor 14, the pressure sensor 15, and the temperature sensor 16 from the corresponding sensor port of the I / O 17d, as necessary, so that the battery at the time of reading is read. Eleven voltages, tire pressure, and tire temperature are identified.

  In the process, the CPU 17a outputs transmission data to the RF transmission unit 13 as necessary. As described above, the transmission data includes the latest specified tire pressure and the latest tire temperature data.

  Here, the transmission timing of the transmission data realized by the processing of the CPU 17a will be described with reference to FIG. FIG. 3 is a timing chart in which the horizontal axis direction is time, and transmission data is transmitted during the time period occupied by each of the rectangles 31a to 31h, and transmission data is not transmitted at other times. Each of the rectangles 31a to 31h corresponds to transmission of one transmission data (hereinafter referred to as a frame).

  In the present embodiment, as illustrated in FIG. 3, an event for transmitting one or a plurality of frames (four in the example of FIG. 3) is executed once for each first period T <b> 1. The first period T1 is, for example, about 1 minute. In each event, one frame is repeatedly transmitted at a second period T2 that is smaller than the first period T1 (for example, 1/1000 or less of the first period T1). The second period T2 is, for example, about 10 milliseconds.

  As will be described later, tire pressure and tire temperature are detected once per event. Accordingly, tire pressure and tire temperature values in a plurality of frames transmitted in one event are the same. And between two different events, the values of tire air pressure and tire temperature in the transmitted frame differ if the detection results in those events are different.

  Here, the internal structure of each of the frames 31a to 31h (hereinafter referred to as the frame 31 as a representative) will be described with reference to FIG. FIG. 4A is a timing chart of the frame 31 with time in the horizontal axis direction. The vertical axis direction indicates transmission on (that is, transmission execution) and transmission off (that is, transmission non-transmission) of the RF transmission unit 13 under the control of the CPU 17a. Execution).

  As illustrated in FIG. 4A, one frame 31 includes a plurality of (for example, 80) data bits 32a to 32k that are transmitted continuously in time. ) Bit string. The tire pressure data and tire temperature data are included in any area of this bit string.

  Here, FIG. 4B illustrates how the voltage of the battery 11 changes when one frame 31 is transmitted. FIG. 4B is a timing chart in which the horizontal axis represents time and the vertical axis represents the voltage of the battery 11. As shown by the solid line 33 in this figure, the voltage of the battery 11 is approximately constant voltage Vin until the time t1 when the transmission of the frame 31 starts, and the period t1 to t2 from the start to the end of the transmission of the frame 31 When the transmission of the frame 31 ends, the voltage Vin before the transmission of the frame 31 is almost restored. Such voltage change characteristics are common to general batteries.

  Thus, the voltage continues to drop during the transmission of the frame 31, and the voltage rises when the transmission of the frame 31 ends. Therefore, at the transmission end time t2 of the frame 31, the voltage of the battery 11 becomes minimum. Hereinafter, the minimum voltage at the transmission end time t2 of the frame 31 is referred to as a termination voltage Vop.

  When this termination voltage Vop is lower than the minimum operating voltage Vmin of the sensor IC 12 shown in FIG. 4B, frame transmission cannot be performed normally. This is because if the voltage of the battery 11 falls below the minimum operating voltage Vmin of the sensor IC 12, problems such as the sensor IC 12 being reset or the sensor IC 12 becoming inoperable occur. If these problems occur during the transmission of the frame 31, the transmission of the frame is terminated halfway. Therefore, it is desirable that the battery 11 and the sensor IC 12 are designed so that the termination voltage Vop is not lower than the minimum operating voltage Vmin as much as possible.

  For example, when the temperature around the tire pressure transmitter 1 (specifically, the temperature of the tire on which the tire pressure transmitter 1 is installed) decreases, the voltage of the battery 11 also decreases. FIG. 5 illustrates the relationship between the termination voltage Vop of the battery 11 and the circuit current (current supplied to the sensor IC 12) at 25 ° C., 0 ° C., −30 ° C., and −40 ° C. Solid lines 41, 42, 43, and 44 correspond to the cases of 25 ° C, 0 ° C, -30 ° C, and -40 ° C, respectively. As shown in this figure, regardless of the circuit current, the termination voltage Vop decreases as the environmental temperature decreases. Such a problem is a problem common to ordinary batteries.

  In view of this problem, the tire pressure transmitter 1 of the present embodiment realizes an operation such that the termination voltage Vop does not fall below the minimum operating voltage Vmin even in an extremely low temperature environment (for example, about −40 ° C.).

  Specifically, the CPU 17a reduces the frequency of frame transmission by reducing the number of frames transmitted in one event in a low temperature environment as compared to the normal environment. The relationship between the frame transmission frequency and the termination voltage Vop will be described below.

  As described above with reference to FIG. 4B, the voltage of the battery 11 decreased by transmitting one frame returns to the voltage Vin before the start of transmission after the end of transmission. However, this return is not perfect. Specifically, the voltage that returns after the end of transmission may be slightly less than the voltage before the start of transmission.

  Therefore, when the tire pressure transmitter 1 repeats frame transmission many times (for example, about several hundred times), the termination voltage Vop gradually decreases and approaches asymptotically to a certain equilibrium voltage. According to the inventors' experiment, this balanced voltage decreases as the frame transmission frequency increases.

  FIG. 6 illustrates the time change of the termination voltage Vop at two frame transmission frequencies. This figure is a graph in which the horizontal axis represents time and the vertical axis represents voltage, and the solid line 34 represents a case where the number of transmission frames per event is 1 in a constant low temperature environment (for example, −40 ° C.). The time change over the long term (for example, 50 hours) of the termination voltage Vop of the battery 11 is shown. In addition, the solid line 35 is a time change over a long period of time (for example, 50 hours) of the termination voltage Vop of the battery 11 when the number of transmission frames per event is four under the same temperature environment as that of the solid line 34. Indicates. However, the event period (that is, the first period T1) is the same in the case of the solid lines 34 and 35.

  As shown in this figure, even if the termination voltage Vop of the battery 11 is initially the same in both cases, as time elapses, when the transmission frequency is higher (corresponding to the solid line 35), the termination voltage Vop drops. Becomes larger. Finally, when the transmission frequency is low (corresponding to the solid line 34), the terminal voltage Vop becomes higher than when the transmission frequency is high.

  FIG. 7 illustrates the relationship between the termination voltage Vop of the battery 11 and the circuit current (current supplied to the sensor IC 12) at two transmission frequencies. When the solid lines 45 and 46 each transmit one frame per minute (ie, one event), this corresponds to the case where four frames are transmitted per minute (ie, one event). As shown in this figure, regardless of the circuit current, the termination voltage Vop decreases as the transmission frequency increases.

  Such a relationship between the transmission frequency and the termination voltage Vop (that is, the voltage of the battery 11 at the timing of the termination portion of the transmission frame) also holds between the transmission frequency and the voltage of the battery 11 at other timings. For example, as the transmission frequency increases, the voltage of the battery 11 at the timing at the start of frame transmission also decreases. However, such a relationship is most prominent between the transmission frequency and the termination voltage Vop.

  As described above, the termination voltage Vop increases as the transmission frequency decreases. Therefore, when the CPU 17a decreases the frame transmission frequency when entering the low temperature environment from the normal environment, the termination voltage Vop is asymptotic. Since the equilibrium voltage approaching becomes larger, the possibility that the termination voltage Vop falls below the minimum operating voltage Vmin is reduced.

  Hereinafter, FIG. 8 shows a flowchart of the program 100 executed by the CPU 17a in order to reduce the frame transmission frequency when entering from a normal environment to a low temperature environment.

  The CPU 17a repeatedly executes this program 100 at the first cycle T1. That is, the program 100 is executed once for each event. In executing the program 100, the CPU 17a first reads the input values to the ports of the I / O 17d corresponding to the pressure sensor 15 and the temperature sensor 16 in step 110, thereby specifying the current tire pressure and tire temperature. .

  Subsequently, in step 120, a frame including the tire pressure and tire temperature data specified in the immediately preceding step 110 is generated. Subsequently, in step 130, transmission processing of the generated frame is started.

  The transmission process of the generated frame is realized by a program separately executed by the CPU 17a in parallel with the process of the program 100. As described above, this transmission processing is processing for transmitting the latest frame a specified number of times in the second cycle T2. In the execution of the program 100, the specified number of times is switched between a normal number of times (for example, four times) and a low temperature number of times (for example, one time) smaller than the normal number of times. When the tire pressure transmitter 1 is shipped from the factory, the CPU 17a employs the normal number of times as the specified number.

  After step 130, the CPU 17a executes a transmission frequency control process once per frame transmission in step 140 until it is determined in step 150 that the frame has been transmitted a prescribed number of times.

  In the transmission frequency control process of step 140, the CPU 17a switches the specified number of times from the normal number of times to the low temperature number based on the fact that the voltage of the battery 11 has fallen below the reference voltage Va. FIG. 9 shows details of this transmission frequency control process.

  As shown in this figure, first, in step 142, the CPU 17a is currently transmitting a frame, and the currently transmitting portion in the frame is the end of the frame (for example, the last one). Bit). If the determination result is affirmative, step 144 is subsequently executed, and if negative, step 142 is executed again.

  In step 144, the current voltage of the battery 11 is read by reading the input value to the port of the I / O 17 d corresponding to the voltage sensor 14. The voltage read here is the voltage of the battery 11 at the timing of the end portion of the frame, that is, the termination voltage Vop.

  Subsequently, in step 146, it is determined whether or not the read termination voltage Vop is smaller than the reference voltage Va. If the terminal voltage Vop is smaller, step 148 is executed. If not smaller, the transmission frequency control process in step 140 is terminated.

  In step 148, the frame transmission frequency is lowered, specifically, the specified number of times is switched from the number of normal times to the number of times of low temperature. However, at this time, the frame period T1 is not changed. After step 148, the transmission frequency control process of step 140 is terminated.

  Thus, the CPU 17a waits for the timing of the end of the frame (see step 142) at each of the multiple frame transmission opportunities in one event (see steps 110 to 130 and 150), and at that timing, the battery 11 Is read (see step 144), and when the read termination voltage Vop falls below the reference voltage Va (see step 146), the frame transmission frequency is lowered by reducing the specified number of times (see step 148). .

  The CPU 17a may apply the specified number of times lowered in step 146 after the next event. In this case, in the current event, frames are transmitted for the normal number of times, and frames are transmitted for the number of times of the low temperature after the next event.

  Alternatively, the CPU 17a may apply the specified number of times lowered in step 146 from the current event. In this case, it is assumed that the frame transmitted when the specified number of times decreases from the normal number of times to the number of times of low temperature is the Nth frame transmitted in the current event, and the number of times of low temperature is M. At this time, if N ≧ M, no further frames are transmitted in the current event. When N <M, the frame is transmitted up to M times in the current event. After the next event, frames are transmitted for the number of times of low temperature.

  Here, the reference voltage Va will be described. The reference voltage Va is a threshold value used for determining whether or not the tire pressure transmitter 1 has entered a low temperature environment from a normal environment. The low temperature environment in which the frame transmission frequency must be reduced is an environment in which the termination voltage Vop is lower than the minimum operating voltage Vmin and the sensor IC 12 is not likely to operate normally. Therefore, it is desirable that the reference voltage Va to be compared with the termination voltage Vop is a value slightly larger than the minimum operating voltage Vmin. For example, the reference voltage Va may be larger than the minimum operating voltage Vmin and not more than 1.2 times the minimum operating voltage Vmin.

For example,
Reference voltage Va = minimum operating voltage Vmin + Vvar + Vtemp
The reference voltage Va determined at the time of manufacturing the sensor IC 12 using the equation may be recorded in the ROM 17c. Here, the value Vvar is the detection accuracy of the voltage sensor 14. The value Vtemp is the maximum voltage drop that can be lowered by the temperature drop in the event period T1.

  This value Vtemp may be a value obtained in the following experiment, for example. That is, an experiment is performed in which the new battery 11 is suddenly moved from a normal temperature environment (for example, 25 ° C.) to a low temperature environment of −40 ° C. In the experiment, the difference X−Y (or the difference X−) between the voltage X of the battery 11 immediately before the transfer to the low temperature environment and the voltage Y of the battery 11 at the time when the period T1 has elapsed since the transfer to the low temperature environment. A range of ± 20% from Y) may be set as the value Vtemp.

  In this case, for example, when the minimum operating voltage Vmin is 1.9 V, the value Vvar is 0.1 v, and the value Vtemp is 0.1 V, the reference voltage Va is 0.2 V larger than the minimum operating voltage Vmin 2 .1V. From another viewpoint, the reference voltage Va is approximately 2.1 / 1.9≈1.1 times the minimum operating voltage Vmin.

  Since the reference voltage Va is higher than the minimum operating voltage Vmin by the value Vvar, the frame is transmitted before the terminal voltage Vop of the battery 11 becomes the minimum operating voltage Vmin regardless of the error in the detection value of the voltage sensor 14. By reducing the frequency, it is possible to avoid a further decrease in the termination voltage Vop.

  Furthermore, since the reference voltage Va is higher than the minimum operating voltage Vmin + value Vvar by the value Vtemp, the termination voltage Vop may fall below the minimum operating voltage Vmin between the current event and the next event. Decrease significantly. That is, there is almost no possibility that the tire pressure transmitter 1 will not operate normally before the frame transmission frequency is lowered at the next event.

  The reference voltage Va may be set to any value within a range including a value of (minimum operating voltage Vmin + Vvar + Vtemp). For example, the reference voltage Va may be set within the range of the minimum operating voltage Vmin <reference voltage Va <(minimum operating voltage Vmin + Vvar + Vtemp) × 1.5, or the minimum operating voltage Vmin + (Vvar + Vtemp) × 0. .5 <reference voltage Va <(minimum operating voltage Vmin + Vvar + Vtemp) × 1.5.

  As described above, the tire pressure transmitter 1 reads the voltage of the battery 11 when the tire pressure information is transmitted (see step 144), and based on the read voltage being lower than the reference voltage Va. Then, the transmission frequency of tire pressure information is reduced (see step 148).

  As described above, the tire pressure transmitter 1 reads the voltage of the battery 11 when the tire pressure information is being transmitted, and the tire pressure information is transmitted when the read voltage falls below the reference voltage. The frequency is decreasing.

  As described above, the voltage of the battery 11 when the tire air pressure information is transmitted is more sensitive to ambient temperature changes than the battery 11 voltage when the tire air pressure information is not transmitted. Change.

  Therefore, by using the voltage of the battery 11 when the tire air pressure information is transmitted, it is possible to accurately detect that the temperature environment should reduce the transmission frequency without depending on the temperature sensor.

  Further, the tire pressure transmitter 1 reads the terminal voltage Vop of the battery 11 at the end of one transmission period of the tire pressure and compares it with the reference voltage Va. In one transmission period of tire pressure, the voltage of the battery 11 continues to decrease, and when the transmission period ends, the voltage of the battery 11 recovers to some extent. Therefore, the voltage of the battery 11 is the lowest at the end of the transmission period.

  As described above, the lower the voltage is, the more sensitive the voltage changes to the surrounding temperature change. Therefore, the end of the transmission period is to detect that the temperature environment should lower the transmission frequency. The detection voltage is optimal.

  The temperature environment in which the transmission frequency should be reduced is a temperature environment immediately before the voltage of the battery 11 starts to fall below the minimum operating voltage of the tire pressure transmitter, as a voltage for detecting such an environment. The voltage in the most lowered state is optimal.

  Further, the tire pressure transmitter 1 includes a ROM 17c as a storage medium for storing the reference voltage Va. The tire pressure transmitter 1 reads the reference voltage Va from the ROM 17c, and the tire terminal pressure Vop falls below the read reference voltage Va. The transmission frequency of air pressure information is reduced.

  As described above, the tire pressure transmitter 1 stores the optimum reference voltage Va corresponding to the minimum operating voltage Vmin of the sensor IC 12 in advance, thereby comparing the detected voltage with the reference voltage Va and transmitting based on the result. When the function for controlling the frequency is created as a program, it is not necessary to change the program for each characteristic of the sensor IC 12, and the program can be shared among the sensor ICs 12 having different characteristics.

  Japanese Patent Application Laid-Open No. 2004-228561 describes a technique for reducing a voltage drop by discharging a capacitor from a capacitor by adding a capacitor in parallel to the battery in order to cope with a problem of a battery voltage drop at a low temperature.

  However, in this method, an additional component called a capacitor is required outside, which causes a problem of increasing the cost. In addition, if a leak current flows through the capacitor, there is a problem that the battery life is deteriorated in the first place. In this embodiment, since there is no configuration in which a capacitor is added in parallel to the battery and the voltage drop is alleviated by discharging from the capacitor, such a problem cannot occur.

  Note that the CPU 17a adopts the reference number of times when the tire temperature read from the output signal of the temperature sensor 16 exceeds the reference temperature (for example, −30 ° C.) when the low temperature number is used as the reference number. It may be set to return to the normal number of times.

  Alternatively, the CPU 17a uses the reference number of times based on the fact that the termination voltage Vop of the battery 11 read from the output signal of the voltage sensor 14 exceeds the return voltage Vr when the number of times at low temperature is adopted as the reference number. May be returned from the number of times of low temperature to the number of times of normal time. In this case, the value obtained by subtracting the minimum operating voltage Vmin from the return voltage Vr may be twice the value obtained by subtracting the minimum operating voltage Vmin from the reference voltage Va.

(Other embodiments)
As mentioned above, although embodiment of this invention was described, the scope of the present invention is not limited only to the said embodiment, The various form which can implement | achieve the function of each invention specific matter of this invention is included. It is.

  For example, in the above embodiment, the CPU 17a changes the number of frames to be transmitted in one event without changing the period T1 between temporally adjacent events in order to lower the frame transmission frequency. However, the method of reducing the frame transmission frequency is not limited to this method, and a method of increasing the period T1 between temporally adjacent events without changing the number of frames transmitted in one event is adopted. May be.

  In the above embodiment, each function realized by the CPU 17a executing a program is realized using hardware having those functions (for example, an FPGA capable of programming a circuit configuration). It may be.

1 is a block diagram showing an overall configuration of a tire pressure monitoring system in an embodiment of the present invention. 1 is a block diagram showing a configuration of a tire pressure transmitter 1. FIG. It is a figure which shows the transmission timing of the data for transmission which the tire pressure transmitter 1 transmits. (A) is a timing diagram showing the structure of one frame 31, and (b) is a timing diagram showing how the voltage of the battery 11 changes during transmission of the frame 31 by the tire pressure transmitter 1. It is a graph which illustrates the relationship between termination voltage Vop and tire temperature. The graph which illustrates the relationship between the time variation of termination voltage, and tire temperature. It is a graph which illustrates the relationship between the termination voltage Vop and the transmission frequency of a frame. It is a flowchart of the program 100 which CPU17a of the control part 17 performs. It is a flowchart which shows the detail of step 140 of the program 100.

Explanation of symbols

1 Tire Pressure Transmitter 3 Display 10 Transmitting Antenna 11 Battery 12 Sensor IC
13 RF transmitter 14 Voltage sensor 15 Pressure sensor 16 Temperature sensor 17 Controller 17a CPU
17b RAM
17c ROM
17d I / O
21 Car body side antenna 22 ECU
31a to 31h Frame 32a to 31k Bit 33 Voltage change

Claims (2)

A tire pressure transmitter that is mounted on a wheel, detects tire pressure of the wheel, and repeatedly transmits information on the detected tire pressure,
A battery (11) for supplying power for transmitting the tire pressure information in the tire pressure transmitter;
Reading means (144) for reading the voltage of the battery (11) at the end of one transmission period of the tire pressure when the tire pressure information is being transmitted;
A tire pressure transmitter comprising: a frequency reduction unit (148) for reducing the transmission frequency of the tire pressure information based on the fact that the voltage read by the reading unit (144) is lower than a reference voltage. A storage medium (17c) for storing the reference voltage;
The frequency reduction means (148) reads the reference voltage from the storage medium (17c), and reduces the transmission frequency of the tire air pressure information based on the fact that the voltage falls below the read reference voltage. The tire pressure transmitter according to claim 1 .

Images