JP5795522B2 - Control device for tire pressure monitoring system - Google Patents

Description

  The present invention relates to a control device for a tire pressure monitoring system.

  Conventionally, a tire pressure monitoring system (TPMS: Tire Pressure Monitoring System) that monitors tire pressure is known. Each tire of a vehicle on which the TPMS is mounted is provided with a sensor unit that detects the tire air pressure. Each sensor unit wirelessly transmits an information signal including a tire air pressure detection result to the in-vehicle device. When the tire pressure falls below a threshold value based on the received information signal, the in-vehicle device warns the user through an indicator.

  For example, in the TPMS described in Patent Document 1, the initialization switch is operated when the tire air pressure is adjusted to the manufacturer's recommended air pressure. Thereby, the vehicle-mounted device shifts to the initialization mode. When the in-vehicle device receives an information signal from each sensor unit in the initialization mode, the in-vehicle device sets a value that is decreased by a certain ratio (for example, 20%) of the tire air pressure included in the signal as a threshold value.

  Here, it is known that the tire air pressure increases as the temperature of the tire increases (Boyle Charles' law). The temperature of the tire varies depending on the outside air temperature and frictional heat with the road during traveling. For this reason, if the temperature of the tire rises after setting the threshold, there is a possibility that no warning will be given even if the air pressure decreases over a certain ratio from the air pressure at that time. Further, since the tire temperature decreases after the threshold value is set, there is a possibility that a warning is issued before the air pressure is reduced by a certain percentage.

  Therefore, for example, in the TPMS described in Patent Document 2, a temperature-corrected threshold value is set. Specifically, the sensor unit is provided with a temperature detection unit that detects the temperature of the tire. The sensor unit wirelessly transmits the detection result of the temperature detection unit to the in-vehicle device. The vehicle-mounted device sets the threshold value in consideration of the tire temperature, which is the detection result of the temperature detection unit. Thereby, an appropriate threshold value is set regardless of the temperature of the tire.

Japanese Patent Laid-Open No. 2003-211925 JP 2003-267011 A

  By the way, as a situation where the tire air pressure falls below a threshold value, there are a case where the tire air pressure gradually leaks over a long period of time (slow depressurization) and a case where the air pressure suddenly decreases due to puncture or the like (rapid depressurization). . As described above, although there are mainly two types of tire pressure reduction modes, the threshold value of TPMS described in Patent Documents 1 and 2 is one. Therefore, it is not possible to set the threshold according to the mode of the tire pressure drop. For this reason, for example, if a threshold value is set in accordance with a slow pressure reduction, even if sudden pressure reduction occurs, no warning is given if the tire air pressure exceeds the threshold value, and the tire air pressure is below the threshold value. The warning could be delayed until On the other hand, if the threshold value is set higher in accordance with the sudden pressure reduction, a quick warning at the time of sudden pressure reduction can be realized, but it is not preferable because a warning is frequently given at the time of slow pressure reduction. In particular, in the case of sudden decompression such as puncture, it is considered that normal traveling of the vehicle is difficult, and therefore, only in the case of sudden decompression, it is required to warn the user more quickly about the decrease in air pressure. .

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a control device for a tire pressure monitoring system that can issue a warning more quickly when the tire pressure suddenly decreases. is there.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
The invention according to claim 1 includes information relating to tire air pressure transmitted from a sensor unit attached to each tire, information relating to the presence or absence of sudden pressure reduction of tire air pressure, and information relating to tire temperature. In the control mode of the tire pressure monitoring system that issues a warning when it is determined that the tire pressure included in the information signal received in the normal mode is equal to or lower than a threshold value, in the initialization mode, When the information signal is received, the boil according to Boyle's law passing through the first point where the tire air pressure and the tire temperature included in the information signal intersect in the relationship between the tire air pressure and the tire temperature. Calculating the Charles straight line, and setting the threshold for slow pressure reduction by reducing the tire air pressure by a predetermined percentage with respect to the boiled Charles straight line A straight line for setting a sudden pressure reduction between the boiled charle line and the slow pressure reducing threshold setting line, and in the normal mode, the tire pressure abruptly increases based on the received information signal. When it is determined that there is depressurization, the tire air pressure at which the tire temperature included in the information signal intersects with the rapid depressurization threshold setting straight line is set as the threshold, and the tire pressure is rapidly depressurized based on the received information signal. When it is determined that there is not, the gist is that the tire air pressure at which the temperature of the tire included in the information signal and the threshold setting line for slow pressure decrease intersect is set as the threshold.

  According to this configuration, the slow pressure-reducing threshold setting line and the sudden pressure-reducing threshold setting line are set. The sudden pressure-reducing threshold setting line is set in a higher tire pressure range than the slow pressure-reducing threshold setting line. When the control device determines that there is a rapid pressure reduction of the tire pressure based on the received information signal, the control device sets a threshold value using the rapid pressure reduction threshold setting straight line, and based on the received information signal, the tire pressure of the tire pressure is set. When it is determined that there is no sudden pressure reduction, a threshold value is set using a slow pressure reduction setting line. Therefore, when the tire air pressure is suddenly reduced, a warning is issued more quickly by setting the threshold value high.

  According to a second aspect of the present invention, in the control device of the tire air pressure monitoring system according to the first aspect, the second point at which the tire air pressure is atmospheric pressure on the boiled charle straight line is calculated, and the first Calculating a third point obtained by reducing the tire air pressure by a certain percentage from the above point, and setting the threshold line for slow pressure reduction so as to pass through the second point and the third point. It is a summary.

  According to this configuration, the slow pressure reducing threshold setting line is set so as to pass through a third point obtained by reducing the tire air pressure by a certain percentage from the first point. Therefore, if the tire temperature is the same as that at the time of initialization, a warning can be reliably issued when the tire air pressure decreases by a certain percentage.

  According to a third aspect of the present invention, in the control device for a tire air pressure monitoring system according to the second aspect, a fourth point between the first point and the third point in the tire air pressure is calculated. The gist of the invention is to set the threshold line for rapid depressurization so as to pass through the second point and the fourth point.

  According to this configuration, the rapid pressure reduction threshold setting line passes through the second point and the fourth point between the first point and the third point. Accordingly, the threshold value setting line for sudden pressure reduction, and the threshold value when the tire air pressure suddenly decreases, is appropriately set.

  ADVANTAGE OF THE INVENTION According to this invention, in the control apparatus of a tire pressure monitoring system, when the tire pressure is suddenly reduced, a warning can be given more quickly.

The block diagram which shows the structure of the tire pressure monitoring system in 1st Embodiment. The graph of the tire air pressure and the tire temperature showing the threshold setting line in the first embodiment. The flowchart which shows the process sequence of CPU of the receiver concerning the warning of the air pressure fall in 1st Embodiment. The flowchart which shows the process sequence of CPU of the receiver in the initialization mode in 1st Embodiment. The graph of the tire air pressure and the tire temperature showing a threshold line for rapid decompression in the second embodiment.

(First embodiment)
Hereinafter, a first embodiment in which a tire pressure monitoring system (TPMS) according to the present invention is embodied will be described with reference to FIGS.

  As shown in FIG. 1, sensor units 30 a to 30 d are provided on the valve portions of the tires of the vehicle 1. Specifically, a sensor unit 30a is provided on the right front wheel, and a sensor unit 30b is provided on the right rear wheel. The left rear wheel is provided with a sensor unit 30c, and the left front wheel is provided with a sensor unit 30d.

(Sensor unit)
The sensor units 30a to 30d are enlarged and shown on the right side of FIG. 1, a CPU (Central Processing Unit) 31, a transmission circuit 32, a transmission antenna 32a, a memory 33, a temperature sensor 34, and an air pressure sensor 35. And comprising. The memory 33 of each sensor unit 30a to 30d stores ID codes ID1 to ID4 unique to each sensor unit.

  The air pressure sensor 35 detects the tire air pressure and outputs the detection result to the CPU 31. The CPU 31 recognizes the tire air pressure based on the detection result from the air pressure sensor 35.

  The temperature sensor 34 detects the temperature of the tire and outputs the detection result to the CPU 31. The CPU 31 recognizes the tire temperature based on the detection result from the temperature sensor 34.

  Further, the CPU 31 determines whether or not there is a sudden pressure reduction based on whether or not the tire air pressure detected through the air pressure sensor 35 has decreased by a certain value or more in a certain time, and based on the determination result, the presence or absence of the sudden pressure reduction is determined. The sudden decompression information shown is generated. The case of sudden pressure reduction is typically the case where puncture occurs, and the case of no sudden pressure reduction is the case where the tire air pressure gradually leaks over a long period of time (slow pressure reduction).

  Then, the CPU 31 generates an information signal including the ID codes ID <b> 1 to ID <b> 4, tire pressure information, tire temperature information, and sudden pressure reduction information at regular intervals, and outputs the information signal to the transmission circuit 32. . The transmission circuit 32 modulates the information signal into a radio wave in the UHF (Ultra High Frequency) band, and wirelessly transmits the signal via the transmission antenna 32a. That is, information signals including different ID codes ID1 to ID4 are transmitted from the sensor units 30a to 30d.

(Receiving machine)
The receiver 10 mounted on the vehicle 1 includes a CPU 11, a receiving circuit 12, a receiving antenna 12 a, a memory 13, and an initialization switch 17. An indicator 15 is connected to the CPU 11. In the memory 13, ID codes ID1 to ID4 unique to the sensor units 30a to 30d are stored in a state associated with tire mounting positions.

  The initialization switch 17 is attached to the vehicle 1 so as to be operable. When operated, the initialization switch 17 outputs an operation signal to that effect to the CPU 11. When receiving an operation signal from the initialization switch 17, the CPU 11 shifts from the normal mode to the initialization mode. In the initialization mode, threshold setting lines L1 and L2 described later are set.

  The receiving circuit 12 receives an information signal via the receiving antenna 12a. Then, the receiving circuit 12 demodulates the received information signal and outputs the demodulated information signal to the CPU 11. Thereby, the CPU 11 recognizes the information signal.

  Here, the memory 13 stores two threshold setting lines L1 and L2 related to the threshold setting. Both threshold setting lines L1 and L2 are set after transition to the initialization mode. As shown in the graph of FIG. 2, both threshold setting lines L1 and L2 intersect at the atmospheric pressure Pa and have a positive slope. The inclination of the threshold setting line L2 for sudden pressure reduction is larger than the inclination of the threshold setting line L1 for gentle pressure reduction. A method of setting the threshold setting lines L1 and L2 will be described in detail later. Based on the threshold setting lines L1 and L2, a threshold value related to a warning about a decrease in tire air pressure is set.

  Hereinafter, a processing procedure related to threshold setting and warning in the CPU 11 will be described with reference to the flowchart of FIG. 3. The flowchart is executed in the normal mode and is started when the CPU 11 recognizes the information signal.

  First, the CPU 11 recognizes the ID codes ID1 to ID4, tire air pressure information, tire temperature information, and sudden pressure reduction information included in the information signal (S101). At this time, the CPU 11 identifies which tire pressure information is based on the ID codes ID1 to ID4 included in the information signal (S102). For example, when the ID code is ID1, it is determined that the information signal is from the sensor unit 30a corresponding to the right front wheel.

  Next, the CPU 11 determines whether or not there is a sudden pressure reduction based on the sudden pressure reduction information (S103). When determining that there is no sudden pressure reduction (NO in S103), the CPU 11 sets a threshold based on the threshold setting line L1 for slow pressure reduction (S104). Specifically, as shown in the graph of FIG. 2, when the CPU 11 recognizes that the temperature of the tire is the temperature T1 based on the temperature information, the tire 11 at the temperature T1 in the threshold setting line L1 for gentle decompression. The air pressure P1 is set to the threshold value Pth1.

  As shown in FIG. 3, when determining that there is a sudden pressure reduction (YES in S103), the CPU 11 sets a threshold based on the threshold setting line L2 for the rapid pressure reduction (S105). Specifically, as shown in the graph of FIG. 2, when the CPU 11 recognizes that the temperature of the tire is the temperature T2 based on the temperature information, the tire 11 at the temperature T2 in the threshold setting line L2 for rapid decompression. The air pressure P2 is set to the threshold value Pth2.

  As shown in FIG. 3, after setting the threshold values Pth1 and Pth2 in step S104 or step S105, the CPU 11 determines whether or not the tire air pressure included in the information signal is equal to or less than the set threshold values Pth1 and Pth2. (S106). When the CPU 11 determines that the tire air pressure is less than or equal to the threshold values Pth1 and Pth2 (YES in S106), the CPU 11 issues a warning through the indicator 15 (S107) and ends the process. When a warning is issued when the tire air pressure is equal to or lower than the threshold value Pth1, it is considered that the tire pressure gradually leaks and is gradually reduced. Further, when a warning is issued when the tire air pressure is equal to or less than the threshold value Pth2, it is considered that the tire air pressure has suddenly decreased due to puncture or the like. Under the condition that the tire temperatures are the same, the threshold Pth2 for sudden pressure reduction is set higher than the threshold Pth1 for slow pressure reduction. Therefore, when the tire air pressure is suddenly reduced, a warning is issued more quickly.

  When the CPU 11 determines that the tire air pressure exceeds the threshold values Pth1 and Pth2 (NO in S106), the CPU 11 terminates the process without giving a warning that the slow or rapid decompression has not occurred.

  Next, a method for setting the threshold setting lines L1 and L2 will be described with reference to the flowchart of FIG. Each process of this flowchart is started by the CPU 11 when the normal mode is shifted to the initialization mode through the operation of the initialization switch 17.

  When the CPU 11 receives the information signal after shifting to the initialization mode (S201), the CPU 11 recognizes the first point A1 where the tire temperature T3 and the tire air pressure P3 included in the signal intersect (S202). Normally, at the time of transition to the initialization mode, the tire air pressure P3 is set to the manufacturer's recommended pressure by the user or a dealer. Then, the CPU 11 calculates a straight line La having an inclination according to Boyle Charles's law passing through the first point A1 (S203). Next, the CPU 11 calculates a second point A2 at which the tire air pressure becomes the atmospheric pressure Pa on the straight line La (S204). Further, the CPU 11 calculates a third point A3 obtained by subtracting, for example, 20% of the air pressure at the first point A1 (S205). Then, the CPU 11 calculates a slow pressure-reducing threshold setting line L1 that passes through the second point A2 and the third point A3 (S206). Next, the CPU 11 calculates an intermediate point A4 between the air pressure at the first point A1 and the air pressure at the third point A3 at the temperature T3 (S207), and passes through the intermediate point A4 and the second point A2. A threshold setting straight line L2 for sudden pressure reduction is calculated (S208). Finally, the CPU 11 stores the calculated threshold setting lines L1 and L2 in the memory 13 (S209), and then ends the process.

  The setting of the threshold setting lines L1 and L2 is executed every time an information signal is received from each of the sensor units 30a to 30d in the initialization mode. Therefore, in this embodiment, different threshold setting lines L1 and L2 are set for each of the sensor units 30a to 30d. That is, the threshold setting lines L1 and L2 are stored after being associated with the sensor units 30a to 30d.

The straight line La corresponds to a boiled charle straight line.
As described above, according to the embodiment described above, the following effects can be obtained.
(1) In the initialization mode, a threshold setting line L1 for slow pressure reduction and a threshold setting line L2 for rapid pressure reduction are set. As shown in the graph of FIG. 2, the rapid pressure reduction threshold setting line L2 is set in a higher tire pressure region than the gentle pressure reduction threshold setting line L1. When the CPU 11 determines that there is a sudden pressure reduction based on the sudden pressure reduction information of the received information signal, the CPU 11 sets a threshold using the threshold pressure setting line L2 for sudden pressure reduction, and there is no sudden pressure reduction based on the sudden pressure reduction information. When the determination is made, the threshold value is set using the threshold setting line L1 for slow pressure reduction. Therefore, when the tire air pressure is suddenly reduced, a warning can be issued more quickly by setting the threshold value high.

  (2) The threshold setting line L1 for slow pressure reduction is set so as to pass through the third point A3 obtained by reducing the tire air pressure from the first point A1 by a certain rate (for example, 20%). Therefore, if the tire temperature is the same as that at the time of initialization, a warning can be reliably issued when the tire air pressure decreases by a certain percentage.

  (3) The threshold setting line L2 for sudden pressure reduction passes through the second point A2 and the intermediate point A4 between the first point A1 and the third point A3. Therefore, the threshold value when the tire air pressure is suddenly reduced is set appropriately.

(Second Embodiment)
Hereinafter, a second embodiment (reference example) of the present invention will be described with reference to FIG. The configuration of this embodiment is the same as that of the first embodiment shown in FIG.

  When the temperature of a tire rises due to outside air temperature or friction with the road while water is in the tire, it is known that the air pressure of the tire increases due to the influence of water vapor evaporated from the water. ing. Considering this, as shown in FIG. 5, the threshold setting line L2 for rapid pressure reduction is set in such a manner that it slides to the high pressure side when the temperature becomes high. Specifically, when the tire temperature reaches the temperature Th1 in the threshold setting line L2 for sudden pressure reduction, the threshold setting line L2 for sudden pressure reduction slides to the high pressure side by the pressure difference ΔP1. The slope of the threshold pressure setting line L2 for rapid pressure reduction in the region higher than the temperature Th1 is the same as that in the region lower than the temperature Th1. Further, when the tire temperature reaches a temperature Th2 higher than the temperature Th1 in the threshold setting line L2 for sudden pressure reduction, the threshold setting line L2 for sudden pressure reduction further slides to the high pressure side by the pressure difference ΔP2. The slope of the threshold pressure setting line L2 for sudden pressure reduction in the region higher than the temperature Th2 is the same as that in the region lower than the temperature Th2. The temperatures Th1 and Th2 are set based on the temperature at which moisture in the tire is expected to evaporate.

  In the present embodiment, for example, when the intermediate point A4 exists between the temperatures Th1 and Th2, the threshold setting line L2 for sudden pressure reduction exceeding the recommended pressure (first point A1), and the threshold value is set. Sometimes it is done.

As described above, according to the embodiment described above, the following effects can be obtained in addition to the effects (1) to (3) of the first embodiment.
(4) It is known that when the temperature of the tire rises while water is contained in the tire, the air pressure of the tire increases due to the influence of water vapor from which the water has evaporated. Considering this, the threshold setting line L2 for sudden pressure reduction is set so that the rate of increase of the tire air pressure with respect to the temperature change increases as the temperature rises. In the present embodiment, the threshold setting line L2 for rapid pressure reduction is set to slide to the high pressure side by the pressure differences ΔP1, ΔP2 at the temperatures Th1, Th2. Thus, when the air pressure of the water-filled tire is high and the air pressure is suddenly reduced by a certain rate (for example, 20%), a warning can be given more reliably.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
In the above embodiments, the threshold setting lines L1 and L2 are set for each of the sensor units 30a to 30d. However, the threshold setting lines L1 and L2 that are common to all the sensor units 30a to 30d are used. A threshold may be set. In this case, for example, threshold setting lines L1 and L2 are set based on the information signal received first in the initialization mode. According to this configuration, it is not necessary to set the threshold setting lines L1 and L2 for each of the sensor units 30a to 30d, so that the processing load on the CPU 11 can be reduced.

  In the above embodiments, the information signals are transmitted from the sensor units 30a to 30d at regular intervals regardless of whether the vehicle is traveling. However, the sensor units 30a to 30d may transmit information signals to the receiver 10 only when the vehicle is traveling. In this case, for example, the sensor units 30a to 30d include acceleration sensors that detect the presence or absence of rotation of the tire as acceleration. Based on the detection result of the acceleration sensor, the CPU 31 transmits an information signal at regular intervals through the transmission circuit 32 and the like only when the tire is rotating.

In addition, an initiator that transmits a request signal that requests the vehicle to transmit an information signal to each sensor unit may be provided.
In the second embodiment, the threshold value straight line L2 for rapid pressure reduction is set to slide to the high pressure side by the pressure differences ΔP1 and ΔP2 at the temperatures Th1 and Th2. The threshold setting straight line L2 for pressure reduction may be slid to the high pressure side. In the second embodiment, the slope of the rapid decompression threshold setting line L2 is constant, but as shown by the alternate long and short dash line in FIG. 5, the temperature is higher than the temperature Th1 in the rapid decompression threshold setting line L2. The slope of the region may be larger than the slope of the low temperature region from the temperature Th1.

  In the second embodiment, the threshold setting line L2 for sudden pressure reduction is set so that the rate of increase in tire air pressure with respect to temperature change increases as the temperature rises. Similarly, the straight line L1 may be set so that the rate of increase in the tire air pressure with respect to the temperature change increases as the temperature rises. Further, even when this configuration is applied only to the configuration of the slow pressure reducing threshold setting line L1 existing as the prior art, an appropriate threshold is set through the slow pressure reducing threshold setting line L1 as in the above (4). be able to.

  In both the above embodiments, the threshold setting line L1 for slow pressure reduction is set so as to pass through the second point A2 and the third point A3. However, the method of setting the threshold setting line L1 for slow pressure reduction is not limited to this, and for example, the air pressure of the line La may be set by decreasing by a certain percentage (for example, 20%).

  In both the above embodiments, the CPU 11 calculates the intermediate point A4 (fourth point) between the first point A1 and the third point A3, and the intermediate point A4 (fourth point) and the second point A threshold setting straight line L2 for sudden pressure reduction passing through the point A2 was calculated. However, the fourth point may be set in addition to the intermediate point as long as it is between the first point A1 and the third point A3.

Next, the technical idea that can be grasped from the embodiment will be described together with the effects.
(B) The control apparatus for tire pressure monitoring system, the rapid decompression threshold setting line is that a the slope is constant, to slide only hot side constant pressure reaches the predetermined temperature.

  (B) Receives an information signal including information related to tire air pressure transmitted from a sensor unit attached to each tire, information related to the presence or absence of sudden pressure reduction of the tire air pressure, and information related to tire temperature. In addition, in the control device of the tire pressure monitoring system that issues a warning when it is determined that the tire pressure included in the information signal received in the normal mode is equal to or less than a threshold value, the information signal is received in the initialization mode. In the relationship between the tire air pressure and the tire temperature, calculate a Boyle Charles straight line according to Boyle Charles's law passing through the first point where the tire air pressure and the tire temperature included in the information signal intersect, A threshold setting line in which the tire air pressure is reduced by a predetermined ratio with respect to the boiled charle straight line is set, and the threshold setting The tire line is set so that the rate of increase in the tire air pressure with respect to the temperature change increases when a certain temperature at which moisture in the tire is expected to evaporate is reached in the relationship between the tire air pressure and the tire temperature. Control device for pneumatic monitoring system.

  It is known that when the temperature of a tire rises in a state where water is contained in the tire, the air pressure of the tire increases due to the influence of water vapor evaporated from the water. Considering this, the threshold setting line is set so that the rate of increase in the tire air pressure with respect to the temperature change increases when the temperature reaches a constant temperature at which moisture in the tire is expected to evaporate. Thereby, even when the air pressure of the water-filled tire is high, the warning can be more reliably performed even when the air pressure is suddenly reduced by a certain rate.

The control device (c) tire pressure monitoring system, the fourth point, it is the midpoint between the third point and the first point.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 10 ... Receiver, 11 ... CPU (control apparatus of TPMS), 17 ... Initialization switch, 30a-30d ... Sensor unit, 31 ... CPU, 34 ... Temperature sensor, 35 ... Air pressure sensor.

Claims (3)

An information signal including information related to the tire air pressure transmitted from the sensor unit attached to each tire, information related to the presence or absence of rapid decompression of the tire air pressure, and information related to the temperature of the tire is received. In the control device of the tire pressure monitoring system that issues a warning when it is determined that the tire pressure included in the information signal received in the mode is equal to or less than a threshold value,
When the information signal is received in the initialization mode, the boil passing through the first point where the tire air pressure and the tire temperature included in the information signal intersect in the relationship between the tire air pressure and the tire temperature. Calculate a boiled Charles straight line according to Charles' law and set a threshold line for slow pressure reduction by reducing the tire air pressure by a predetermined ratio to the boiled Charles straight line. Set the threshold setting line for sudden decompression between the threshold setting lines,
In the normal mode, when it is determined that there is a rapid depressurization of the tire air pressure based on the received information signal, the tire temperature included in the information signal intersects with the rapid depressurization threshold setting line. When it is determined that there is no rapid pressure reduction of the tire pressure based on the received information signal, the tire pressure at which the tire temperature included in the information signal intersects the slow pressure reduction threshold setting line A control device for a tire air pressure monitoring system that uses the threshold value. In the control device of the tire pressure monitoring system according to claim 1,
A second point at which the tire air pressure is atmospheric pressure on the boiled charle straight line is calculated, and a third point obtained by reducing the tire air pressure by a certain percentage from the first point is calculated, and the slow pressure reduction A control device for a tire air pressure monitoring system that sets a threshold setting line so as to pass through the second point and the third point. In the control device of the tire pressure monitoring system according to claim 2,
A fourth point between the first point and the third point in the tire air pressure is calculated, and passes through the second point and the fourth point through the rapid decompression threshold setting line. Control device for tire pressure monitoring system to be set as follows.