JP2010241384A - Tire pressure monitoring system and tire pressure monitoring unit - Google Patents

Abstract

A tire pressure monitoring system is provided that prevents a state in which a transmission frequency is high from continuing unnecessarily and prevents a battery of a tire pressure sensor unit from being consumed at an early stage.
A tire air pressure monitoring system 100 is mounted on a wheel 6 of a vehicle 1 to detect the air pressure of a tire 2 and transmit monitoring data including the air pressure data at an autonomous predetermined frequency. 3 and a tire air pressure monitoring unit 5 mounted on the vehicle 1 for monitoring monitoring data and detecting a decrease in air pressure. When the vehicle body speed of the vehicle 1 is equal to or higher than a predetermined threshold, the tire pressure monitoring unit 5 transmits a transmission command to the tire pressure sensor unit 3 at a frequency higher than an autonomous predetermined frequency, and the tire pressure sensor unit 3 Every time a transmission command is received, monitoring data is returned.
[Selection] Figure 1

Description

  The present invention relates to a tire pressure monitoring system and a tire pressure monitoring unit that can easily identify a tire whose air pressure has dropped.

  Tire Pressure Monitoring System (TPMS) is a system that monitors tire pressure and allows the vehicle driver to quickly recognize when the tire pressure drops while driving, In North America, it is already required to be installed in newly sold vehicles.

  There are two types of TPMS: indirect and direct (sensor type). The indirect TPMS detects the difference in the outer diameter of the tire depending on the size of the air pressure from the difference in rotational speed, and estimates the air pressure. In the direct type TPMS, for example, a sensor unit integrated with an air valve is attached to each wheel, and the air pressure of each tire is directly measured by the sensor.

  The direct TPMS has a pneumatic sensor unit on the tire (wheel) side and an in-vehicle ECU (Electronic Control Unit, vehicle body side unit) on the vehicle body side. Each unit has a wireless communication function. For example, the units communicate with each other (or communicate in one direction) and wirelessly transmit tire pressure data directly measured by the air pressure sensor unit to the in-vehicle ECU. The in-vehicle ECU receives the transmitted tire air pressure data, processes it, and notifies the driver of the decrease in air pressure. In the following description, TPMS refers to a direct (sensor type) TPMS having a wireless transmission / reception function.

  In this TPMS, the in-vehicle ECU can not only detect that an abnormality in air pressure has occurred in any of a plurality of tires provided in its own vehicle, but can also detect a decrease in air pressure by specifying individual tires. preferable. In so-called luxury cars, a TPMS for identifying and alarming a tire in which a drop in air pressure has occurred is often mounted. In such a TPMS, in order to control the air pressure sensor unit of a specific tire, an initiator is arranged for each tire house of each wheel on the vehicle side, and a modulation magnetic field of each LF (long wave) band is generated, and a target air pressure is generated. A command signal is transmitted to the sensor unit.

  When traveling at an ordinary speed, it is sufficient if the tire pressure data is obtained from the air pressure sensor unit at a normal frequency (for example, once every minute). When driving at a very high speed (e.g., 270 km / h or more) far exceeding the typical speed, if the tire pressure data can only be obtained at a normal frequency, the driver is not aware of the low pressure condition. , Run a long distance. However, if tire pressure data is constantly transmitted from the air pressure sensor unit at a high frequency (for example, 4 times per minute) in preparation for high-speed driving, the air pressure data transmission frequency is excessive at daily speeds. The battery built in the air pressure sensor unit will be consumed quickly.

  Therefore, it has been required to achieve both the promptness of tire pressure data during high-speed driving and the long life of the built-in battery during daily life. For example, in order to promptly notify the driver of a decrease in tire air pressure during high speed traveling, a tire air pressure monitoring device is disclosed that increases the transmission frequency of the air pressure signal transmitted from the air pressure sensor during high speed traveling (Patent Document 1). reference).

JP 2005-1112017 A

  However, according to the tire pressure monitoring device described in Patent Document 1, first, when the wheel speed increases, an instruction to shorten the transmission interval of the air pressure signal is issued from the vehicle body side transmission / reception antenna to the wheel side air pressure sensor. The transmission interval becomes shorter. Thereafter, when the wheel speed decreases, an instruction to return (longen) the air pressure signal transmission interval is issued. If this “return” instruction is not normally received by the wheel side air pressure sensor, the transmission interval is not released even though the wheel speed is slow, and the air pressure signal is frequently released. Will continue to be transmitted, and there is a problem that the battery power supply with a built-in air pressure sensor is consumed quickly.

  Therefore, the present invention solves the above-mentioned problems, and a tire pressure monitoring system and a tire that can achieve both high-frequency monitoring data transmission during high-speed driving and early battery consumption prevention in the tire pressure sensor unit. An object is to provide an air pressure monitoring unit.

In order to solve the above-described problems, a tire pressure monitoring system according to the present invention includes a tire pressure sensor unit that is mounted on a tire or a wheel of a vehicle and detects the pressure of the tire, and a tire pressure sensor unit that is mounted on the vehicle. A tire pressure monitoring unit that monitors the monitoring data that is transmitted and that includes the data of the air pressure and detects a decrease in the air pressure.
The tire pressure monitoring unit transmits a transmission command to the tire pressure sensor unit at a frequency corresponding to the vehicle body speed, and the tire pressure sensor unit transmits monitoring data each time the transmission command is received.

  Further, the tire pressure monitoring unit according to the present invention (Claim 3) provides a transmission command for forcibly returning the monitoring data when the vehicle body speed of the vehicle is equal to or higher than a predetermined threshold value. Is transmitted to the tire air pressure sensor unit at a frequency higher than the frequency of, and the monitoring data is forcibly returned to the tire air pressure sensor unit every time a transmission command is transmitted.

  ADVANTAGE OF THE INVENTION According to this invention, the tire pressure monitoring system and tire pressure monitoring unit which can be compatible with the transmission of the monitoring data with high frequency at the time of high-speed driving | running | working and the early consumption prevention of the battery built in the tire pressure sensor unit can be provided.

1 is a perspective plan view schematically showing a vehicle equipped with a tire pressure monitoring system according to an embodiment of the present invention. It is a block diagram which shows a tire pressure sensor unit in detail. It is a graph which shows the relationship between the vehicle body speed in the tire pressure monitoring system of this embodiment, and the transmission frequency of the monitoring data of a tire. It is a flowchart which shows the execution pattern of the control mode by a tire pressure monitoring unit.

Next, one mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described in detail with reference to the accompanying drawings.
FIG. 1 is a perspective plan view schematically showing a vehicle 1 equipped with a tire pressure monitoring system 100 according to an embodiment of the present invention.
The vehicle 1 is a four-wheel vehicle including four wheels 6FR (right front wheel), 6FL (left front wheel), 6RR (right rear wheel), and 6RL (left rear wheel). Four tires 2FR, 2FL, 2RR, 2RL are mounted on the four wheels 6FR, 6FL, 6RR, 6RL, respectively.

  In the present embodiment, with reference to the traveling direction of the vehicle 1, “FR” is used for the right front component, “FL” is used for the left front component, “RR” is used for the right rear component, The character string “RL” is placed after the component to indicate the arrangement position of the component. When these components are collectively referred to, and when these components are not distinguished by their arrangement positions, they are indicated by the main body part (numerical part) of the code without the letters FR, FL, RR, RL. To do. In this case, for example, the tire 2 and the wheel 6 are described.

  The tire air pressure monitoring system 100 is constructed in the vehicle 1 and promptly notifies the driver when the air pressure drop occurs in the tire 2. The tire air pressure monitoring system 100 includes a vehicle body side component of the vehicle 1 and a wheel 6 side configuration. It has elements. The components on the wheel 6 side include a tire pressure sensor unit 3 (3FR, 3FL, 3RR, 3RL). The components on the vehicle body side include a tire pressure monitoring unit 5, an initiator 10 (10FR, 10FL, 10RR, 10RL), an indicator 4, a vehicle speed sensor 51, and a receiving antenna 52.

  In order to directly measure the air pressure of the four tires 2FR, 2FL, 2RR, and 2RL, the wheels 6FR, 6FL, 6RR, and 6RL are provided with tire pressure sensor units 3FR, 3FL, 3RR, and 3RL, respectively. The tire pressure sensor units 3FR, 3FL, 3RR, 3RL may be provided in the tires 2FR, 2FL, 2RR, 2RL.

The appearance of the tire pressure sensor unit 3 is shown in the upper right of FIG.
The tire pressure sensor unit 3 is a valve-integrated type, but a separate type can also be used. One end of the tire valve 37 is integrally fixed to the main body portion so as to open into an air hole 38 formed in the main body portion. The other end of the tire valve 37 is exposed to the outside of the rim (described later) and is provided with an air inlet, but a valve cap is usually fitted. A sensor hole 39 is also formed in the main body portion, and sensors built in the main body portion can measure the environment (pressure, temperature, etc.) in the tire 2.

  When assembling the wheel 6, first, the main body portion of the tire pressure sensor unit 3 is directed in a direction in which the air hole 38 and the sensor hole 39 are opened toward the hollow portion side (air chamber side) of the tire 2. Then, the valve stem of the tire valve 37 is passed from the inner side of the rim of the wheel 6 through the valve mounting hole of the rim to the outer side (the side that contacts the outside air) of the rim, and the grommet at the base of the tire valve 37 is passed. The rim is clamped with the flange of the inner valve stem and the outer washer and the valve nut to fix the tire valve 37 to the rim in an airtight manner. Thereafter, the tire 2 is assembled to the rim of the wheel 6, air is injected from the air inlet of the tire valve 37 to a specified pressure, and finally a valve cap is fitted.

  Since the tire valve 37 protrudes outward from the rim of the wheel 6, an antenna is incorporated therein, or the tire valve 37 itself serves as an antenna for the tire pressure sensor unit 3. Alternatively, the antenna may be incorporated in a resin or rubber grommet at the base of the tire valve 37. The internal configuration of the tire pressure sensor unit 3 will be described later with reference to FIG.

  The tire pressure monitoring unit 5 is an ECU (Electronic Control Unit) and includes a microcomputer and peripheral devices, and implements each function described later by installing a predetermined program in the microcomputer so as to be executable. . The tire pressure monitoring unit 5 is connected to a vehicle speed sensor 51, an initiator 10 (10FR, 10FL, 10RR, 10RL), a receiving antenna 52, and an indicator 4.

  Initiators 10FR, 10FL, 10RR, 10RL are installed in tire houses containing tires 2FR, 2FL, 2RR, 2RL, respectively, and are controlled by tire pressure monitoring unit 5 to tire pressure sensor units 3FR, 3FL, 3RR, 3RL. For example, it has a function of transmitting a command signal by an amplitude modulation magnetic field having a frequency of 125 kHz.

In the present embodiment, the command signals transmitted from the tire pressure monitoring unit 5 to the tire pressure sensor unit 3 through the initiator 10 include the “start command”, “pause command”, and “transmission command”. These three command signals are originally provided in the tire pressure monitoring system 100.
Among these, the “start command” is a command signal for starting the tire pressure sensor unit 3 that has been stopped. The “pause command” is a command signal for pausing the activated tire pressure sensor unit 3. The “transmission command” is a command signal for forcibly returning one monitoring data to the activated tire pressure sensor unit 3.

  The “start-up command” is transmitted through the initiator 3 when the ignition switch of the vehicle 1 is turned on. The “pause command” is transmitted through the initiator 3 when the ignition switch of the vehicle 1 is turned off. In this embodiment, the “transmission command” is continuously transmitted through the initiator at a short time interval (high frequency) when the vehicle body speed of the vehicle 1 is equal to or higher than a predetermined threshold, and when the vehicle body speed is lower than the predetermined threshold. Will stop sending.

  When the “start command” is received, the tire pressure sensor unit 3 in the resting state starts and enters an operating state. During the operation state, the tire pressure sensor unit 3 transmits monitoring data each time a built-in transmission timer (not shown) measures a predetermined time (for example, 1 minute). That is, the tire pressure sensor unit 3 autonomously transmits monitoring data (the built-in battery 35 is consumed). When the “pause command” is received, the tire pressure sensor unit 3 in the operating state enters the dormant state. During the resting state, the tire pressure sensor unit 3 stops the operation of other functions except for the minimum function for receiving the start command and starting again (consumption of the built-in battery 35 is prevented / suppressed). ). When the “transmission command” is received, the tire pressure sensor unit 3 returns monitoring data each time, regardless of the timing of the transmission timer. At the same time, the transmission timer of the tire pressure sensor unit 3 is reset and starts counting again from zero. Incidentally, the tire pressure sensor unit 3 may be configured to forcibly return a plurality of monitoring data, for example, to return two monitoring data continuously by one reply.

  The vehicle body speed sensor 51 generates a vehicle body speed signal representing the vehicle body speed of the vehicle 1 from the rotational speed of the final gear of the drive shaft, for example, and transmits it to the tire air pressure monitoring unit 5. The vehicle body speed does not indicate the vehicle body speed in a strict sense, but may be a wheel speed.

  The receiving antenna 52 has a function of receiving monitoring data transmitted from the tire pressure sensor units 3FR, 3FL, 3RR, 3RL, for example, by radio waves in the UHF band (ultra-high frequency band) and sending the monitoring data to the tire pressure monitoring unit 5.

  The tire pressure monitoring unit 5 has a function of demodulating the monitoring data and extracting the monitoring data. One frame of monitoring data includes a sensor ID and measurement data (air pressure data, temperature data, etc.). The sensor ID is very unique data (unique in many vehicles 1), and the sensor IDs of the tire pressure sensor units 3FR, 3FL, 3RR, 3RL are registered in the tire pressure monitoring unit 5 in advance.

  The indicator 4 is a display device that performs display according to the control of the tire pressure monitoring unit 5. As shown in the indicator display example 40, when a tire abnormality such as a decrease in the air pressure of the tire 2 is detected, a tell tale 43 in which the “!” Mark is combined with the cross-sectional shape of the tire 2 is controlled according to the control of the tire air pressure monitoring unit 5. While lighting in yellow, the portion corresponding to the tire 2 corresponding to the vehicle-shaped symbol 41 is lit in yellow to notify the driver. When any system abnormality occurs in the tire pressure monitoring system 100, the “TPMS” tell tale 44 is lit in yellow.

FIG. 2 is a block diagram showing the tire pressure sensor unit 3 in detail.
The tire pressure sensor unit 3 includes a microprocessor 30 that controls and controls the tire pressure sensor unit 3, a reception antenna 310 that receives a signal from the initiator 10, and a wireless reception unit 31 that demodulates a reception signal from the reception antenna 310. A wireless transmission unit 32 that modulates transmission data from the microprocessor 30, a transmission antenna 320 that transmits a transmission signal from the wireless transmission unit 32 to the reception antenna 52 of the tire pressure monitoring unit 5, and static pressure in the tire 2. Power is supplied to each part of the tire pressure sensor unit 3 including the pressure sensor 33 that outputs as a physical quantity such as electric capacity, the temperature sensor 34 that outputs the temperature inside the tire 2 as a physical quantity such as a resistance value, and the microprocessor 30. And a battery 35.

The microprocessor 30 includes a CPU 301, a main storage unit 302 including a RAM, an auxiliary storage unit 303 including a ROM (including an EEPROM), and an I / O (input / output unit) that controls input / output in the microprocessor 30. ) 304, and an AD converter 305 that converts analog measurement values obtained by sensors such as the pressure sensor 33 and the temperature sensor 34 into digital data.
In the microprocessor 30, a predetermined program and data are stored in the auxiliary storage unit 303, and the program and data are loaded into the main storage unit 302 and executed by the CPU 301 to exhibit a predetermined function.

  As described above, in the present embodiment, when the vehicle body speed of the vehicle 1 is less than the threshold, the tire air pressure sensor unit 3 causes the transmission timer to measure a predetermined period (that is, at a low frequency; for example; Monitoring data autonomously (once every minute). On the other hand, when the vehicle body speed of the vehicle 1 is equal to or higher than the threshold value, a transmission command for requesting transmission (reply) of monitoring data from the tire pressure monitoring unit 5 through the initiator 10 each time (at a high frequency; for example, Send 8 times per minute). For this reason, the tire pressure sensor unit 3 responds to each transmission command only once and returns monitoring data each time.

FIG. 3 is a graph showing the relationship between the vehicle body speed and the transmission frequency of the monitoring data of the tire 2 in the tire pressure monitoring system 100 of the present embodiment.
When the vehicle body speed of the vehicle 1 is less than a threshold (for example, 270 km / h), the monitoring data may be transmitted at a low frequency of once every minute, for example.
When the vehicle body speed of the vehicle 1 is a high speed equal to or higher than a threshold value (for example, 270 km / h), the tire 2 is deteriorated in durability when the air pressure is low. Therefore, the monitoring data is transmitted every minute, for example. 8 times.
Incidentally, at 270 km / h or more, the nail stabbed in the tire 2 is easily removed by centrifugal force.
The total amount of time that the vehicle 1 travels at such a vehicle body speed that is equal to or higher than the threshold value is usually very limited in view of the life of the vehicle 1, and therefore the frequency only when the vehicle 1 travels at a high speed that is equal to or higher than the threshold value. Even if it raises, it has little influence on the lifetime of the battery 35. Further, when the vehicle 1 travels at a high speed equal to or higher than the threshold value, transmission is performed at a high frequency, and the result is reflected to promptly notify the driver of a decrease in air pressure. Avoiding long distances while falling.

  Note that the frequency when the vehicle body speed of the vehicle 1 exceeds the threshold value is not fixed to 8 times per minute, but may be changed continuously or stepwise according to the vehicle body speed. Good. By the way, for example, in the example of FIG. 3, if it exceeds 270 km / h, the frequency is increased to 8 times per minute, but if it exceeds 300 km / h, it increases to 10 times per minute, for example. That is.

FIG. 4 is a flowchart showing an execution pattern of the control mode by the tire pressure monitoring unit 5.
The tire air pressure monitoring unit 5 refers to the vehicle body speed signal from the vehicle body speed sensor 51, and determines whether or not the vehicle body speed of the vehicle 1 is greater than or equal to a threshold value (step S1).

  When the vehicle body speed is not equal to or higher than the threshold (when it is lower than the threshold) (No in step S1), the normal initiate mode is performed (step S3). That is, the tire pressure sensor unit 3 autonomously transmits monitoring data to the tire pressure monitoring unit 5 autonomously, for example, when measuring 1 minute (that is, at a low frequency of once per minute). And it returns to step S1 and repeats a process similarly.

  When the vehicle body speed is equal to or higher than the threshold value (Yes in step S1), the high-frequency initiate mode is performed (step S2). That is, the tire pressure monitoring unit 5 transmits a transmission command to the tire pressure sensor unit 3 at a high frequency of, for example, eight times per minute. As a result, the tire pressure sensor unit 3 receives the transmission command every time, that is, For example, the monitoring data is returned to the tire pressure monitoring unit 5 at a high frequency of 8 times per minute. And it returns to step S1 and repeats a process similarly.

  The high-frequency initiate mode (step S2) is used when the vehicle body speed is equal to or greater than the threshold value even when the normal initiate mode (step S3) is being performed (while the transmission timer of the tire pressure sensor unit 3 is measuring) ( Yes in step S1), and is performed with priority.

To supplementarily explain the present embodiment, when the vehicle body speed is less than a predetermined threshold, the tire pressure sensor unit 3 is autonomous in accordance with a built-in transmission timer, for example, at a low frequency (normal frequency) once a minute. Monitoring data is being sent to
On the other hand, when the vehicle body speed is equal to or higher than a predetermined threshold, a transmission command is frequently transmitted from the tire pressure monitoring unit 5 to the tire pressure sensor unit 3 through the initiator 10. For this reason, the tire pressure sensor unit 3 returns monitoring data every time in response to the transmission command. Incidentally, in this embodiment, a transmission command is transmitted to the tire pressure sensor unit 3 at a frequency of 8 times per minute. For this reason, the tire pressure sensor unit 3 returns monitoring data to the tire pressure monitoring unit 5 at a frequency of eight times per minute. The tire pressure sensor 3 resets the above-described transmission timer when receiving the transmission command. For this reason, in this embodiment, if the vehicle body speed is equal to or higher than a predetermined threshold value, autonomous monitoring data transmission by the tire pressure sensor unit 3 at one minute intervals is not substantially performed.

  By the way, instead of the method of transmitting the transmission command to the tire pressure sensor unit 3 through the initiator 10 at a high frequency and receiving the monitoring data that is forcibly returned as in the present embodiment, another command signal is transmitted through the initiator 10. A comparative example in which the transmission frequency of the autonomous monitoring data of once per minute is changed to a high frequency of, for example, eight times per minute by transmitting to the tire pressure sensor unit 3 is also conceivable. In the case of this comparative example, the command signal for increasing the autonomous transmission frequency and the command signal for returning the transmission frequency to the normal frequency once per minute are required. The number of types must be increased. For this purpose, not only the function of the tire pressure monitoring unit 5 but also the function of the tire pressure sensor unit 3 must be changed.

  In contrast, in the present embodiment, the transmission command is a command signal originally provided in the tire pressure monitoring system 100, and simply changes the transmission frequency depending on whether the vehicle body speed is equal to or higher than a predetermined threshold value. Changing the function of the tire pressure monitoring unit 5 becomes much simpler than increasing the types of command signals. Moreover, it is not necessary to change the function of the tire pressure sensor unit 3.

  Furthermore, in the comparative example, if the command signal for returning the transmission frequency is not successfully received by the tire pressure sensor unit 3 when the vehicle body speed is less than the predetermined threshold, the vehicle body speed is less than the predetermined threshold. Even so, the tire pressure sensor unit 3 will continue to transmit monitoring data at a high frequency, and the consumption of the battery 35 will be greatly accelerated. In addition, in the comparative example, if the command signal for changing the transmission frequency to a high frequency is not successfully received by the sensor unit when the vehicle body speed exceeds the predetermined threshold value, the vehicle body speed exceeds the predetermined threshold value. However, the tire pressure sensor unit 3 transmits monitoring data at a normal frequency, and cannot achieve the purpose of monitoring at a high frequency during high-speed traveling.

  On the other hand, in the present embodiment, since the transmission command is transmitted to the tire pressure sensor 3 at a high frequency, the command signal for increasing the transmission frequency is not successfully received in a single manner as in the comparative example. Also, inconvenience due to the fact that the command signal for returning the transmission signal to the original is not successfully received is avoided.

  In other words, according to the present embodiment, the tire pressure monitoring system 100 and the tire pressure monitoring that can both transmit monitoring data at a high frequency during high-speed traveling and prevent early consumption of the battery 35 built in the tire pressure sensor unit 3. The unit 5 can be provided at low cost and with high reliability.

  In addition, although the example which resets the timer at the time of receiving monitoring data autonomously when it receives a transmission command and resets it to zero has been shown, autonomous transmission of monitoring data and forced reply without resetting the timer May be mixed. This case also belongs to the technical scope of the present invention.

1 Vehicle 2 (2FR, 2FL, 2RR, 2RL) Tire 3 (3FR, 3FL, 3RR, 3RL) Tire pressure sensor unit 5 Tire pressure monitoring unit 6 (6FR, 6FL, 6RR, 6RL) Wheel 10 (10FR, 10FL, 10RR) , 10RL) Initiator 30 Microprocessor 31 Wireless receiver 32 Wireless transmitter 33 Pressure sensor 51 Vehicle speed sensor 52 Receiving antenna 100 Tire pressure monitoring system 310 Receiving antenna 320 Transmitting antenna

Claims (3)

A tire pressure sensor unit that is mounted on a tire or a wheel of a vehicle, detects the air pressure of the tire, and autonomously transmits monitoring data including the air pressure data at a predetermined frequency, and is mounted on the vehicle and the monitoring A tire pressure monitoring system comprising: a tire pressure monitoring unit that monitors data and detects a decrease in the air pressure;
The tire pressure monitoring unit transmits a monitoring data transmission command to the tire pressure sensor unit at a frequency higher than the autonomous predetermined frequency when the vehicle body speed of the vehicle is equal to or higher than a predetermined threshold,
The tire pressure sensor unit returns the monitoring data each time the transmission command is received regardless of the autonomous predetermined frequency.
Tire pressure monitoring system characterized by that.   2. The tire pressure according to claim 1, wherein when the vehicle body speed is equal to or higher than a predetermined threshold, the tire air pressure monitoring unit further increases the frequency of transmitting the transmission command according to the increase in the vehicle body speed. Monitoring system. Tire data of a vehicle or a tire pressure sensor unit mounted on a wheel receives monitoring data autonomously transmitted at a predetermined frequency, monitors tire air data included in the received monitoring data, and In the vehicle-mounted tire pressure monitoring unit that detects the decrease state of
The tire pressure sensor unit has a function of transmitting a transmission command for forcibly returning the monitoring data,
When the vehicle body speed of the vehicle is equal to or higher than a predetermined threshold, the transmission command is transmitted to the tire pressure sensor unit at a frequency higher than the autonomous predetermined frequency, and each time the transmission command is transmitted, Monitoring data is forcibly returned to the air pressure sensor unit, and the forcibly returned monitoring data is used to detect a decrease in the air pressure.
A tire pressure monitoring unit characterized by that.

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