JP2012206679A - Receiver of tire air pressure monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To automatically execute initialization in a receiver of a tire air pressure monitoring system.SOLUTION: A rapid pressure reduction detection threshold value Th1 is automatically updated from an initial value in accordance with the rise in an air pressure. When adjustment of the tire air pressure is performed, the rapid pressure reduction detection threshold value Th1 is made to be the initial value equal to a low air pressure detection threshold value Th2, and is initialized. Thus, initialization is executed for each of the prescribed cycles, and the rapid pressure reduction detection threshold value Th1 corresponding to the pressure varying in accordance with an outside air temperature can be automatically set.

Description

  The present invention relates to a receiver 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 TPMS is mounted is provided with a sensor unit that detects tire air pressure. Each sensor unit transmits an information signal including a tire air pressure detection result to the vehicle-mounted 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 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.

Japanese Patent Laid-Open No. 2003-211925

  In the configuration described in Patent Document 1, the threshold is set by the user operating the initialization switch. Here, it is known that the tire air pressure increases as the temperature rises (Boyle Charles' law). Therefore, the air pressure of the tire varies according to the change in the outside air temperature accompanying the change in season. For example, it is assumed that the threshold is set through the operation of the initialization switch when the outside air temperature is high. Thereafter, when the outside air temperature decreases, the tire air pressure decreases according to the above rule even if there is no leakage of the tire air pressure. In this case, before the tire air pressure decreases by a certain percentage, there is a risk that the air pressure falls below the threshold value and a warning of a decrease in air pressure is issued.

  On the other hand, when the outside air temperature rises, there is a possibility that a warning about a decrease in air pressure will not be given even if the tire air pressure decreases beyond a certain rate. Although the above problem is solved by the user operating the initialization switch at regular intervals, it is not preferable to force the user to perform such an operation on a regular basis.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a receiver for a tire pressure monitoring system that is automatically initialized.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
According to a first aspect of the present invention, there is provided a receiver for a tire pressure monitoring system that issues a warning when a tire pressure included in an information signal from a sensor unit attached to each tire falls below a first threshold. The first threshold value is updated from the initial value according to the change in air pressure due to the temperature change of the tire, and after the tire air pressure fluctuates more than a certain value within a certain time with the air pressure adjustment, the first threshold value is The gist is to set the initial value.

  According to this configuration, the first threshold value is automatically updated from the initial value as the air pressure varies. When the adjustment of the tire air pressure is executed, the first threshold value is initialized to be an initial value. Thereby, initialization is performed each time the air pressure is adjusted, and the first threshold value corresponding to the pressure that changes with the outside air temperature can be automatically set.

  According to a second aspect of the present invention, in the receiver of the tire pressure monitoring system according to the first aspect, in addition to the first threshold value, a second threshold value that is the same value as the initial value is set as a fixed value. When the air pressure is suddenly reduced, a warning is given when the air pressure falls below the first threshold, and a warning is also given when the tire air pressure falls below the second threshold except when the air pressure is suddenly reduced. The gist is to do.

  According to this configuration, two threshold values are properly used as necessary. For example, when the tire is punctured, a warning is issued when the tire air pressure drops below the first threshold due to sudden pressure reduction. Therefore, a warning related to tire puncture can be promptly performed.

  The second threshold is a fixed value. Therefore, it is not necessary to set the second threshold value by operating the initialization switch after adjusting the air pressure to an appropriate value as in the prior art. Therefore, convenience is improved. Further, since the second threshold value does not depend on the air pressure adjusted by the user, the second threshold value can be prevented from being set low or high by adjusting the air pressure to be inappropriate by the user. Thereby, when the tire air pressure naturally leaks, a warning can be given at an appropriate timing.

  According to a third aspect of the present invention, in the receiver of the tire pressure monitoring system according to the first or second aspect, the tire air pressure included in the information signal is finally set to the first threshold value as the initial value. The gist of the present invention is to update the first threshold value to a value that is reduced by a certain rate with respect to the maximum value when the maximum value is in the period from the start to the present.

  According to this configuration, when the tire air pressure reaches the maximum value, the first threshold value is updated to a value that is decreased by a certain percentage with respect to the air pressure. Thereby, even when the air pressure increases due to the temperature rise of the tire, a warning can be reliably issued when the tire air pressure decreases (rapid pressure reduction) by a certain rate.

  According to the present invention, initialization can be automatically performed in the receiver of the tire pressure monitoring system.

The block diagram of a tire pressure monitoring system. The graph which shows the fluctuation | variation of an air pressure. The enlarged view of the range A of FIG. (A) in the CPU of the vehicle is a flowchart showing a processing procedure relating to updating of the sudden pressure reduction detection threshold, and (b) is a flowchart showing a processing procedure relating to initialization of the sudden pressure reduction detection threshold.

Hereinafter, an embodiment in which a receiver of 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, a sensor unit 30 is provided in the valve portion of each tire of the vehicle 1. The sensor unit 30 includes a pressure sensor 33, a CPU (Central Processing Unit) 31, a transmission circuit 32, and a transmission antenna 32a as shown in an enlarged view on the lower side of FIG.

  The pressure sensor 33 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 pressure sensor 33. Then, the CPU 31 generates an information signal including tire air pressure information at regular intervals, and outputs the information signal to the transmission circuit 32. The transmission circuit 32 modulates the information signal and transmits the signal as a radio signal via the transmission antenna 32a.

  Based on the detection result from the pressure sensor 33, the CPU 31 adds a sudden decompression bit to the information signal when the pressure is reduced by a certain pressure over a certain time, and sends the information signal to the transmission circuit 32 and the transmission antenna 32a. Via wireless transmission. The constant time and the constant pressure are determined based on the manner in which the air pressure decreases when the tire is punctured.

  The receiver 10 mounted on the vehicle 1 includes a CPU 11, a receiving circuit 12, a receiving antenna 12 a, and a memory 13. An indicator 15 is electrically connected to the CPU 11.

  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. The CPU 11 recognizes the tire air pressure based on the demodulated information signal.

  The memory 13 stores a threshold value related to a tire pressure drop warning and a maximum tire pressure value after initialization. In this example, as shown in FIG. 2, a sudden pressure reduction detection threshold Th1 and a low air pressure detection threshold Th2 are set as thresholds. The low air pressure detection threshold Th2 is set as a fixed value based on the manufacturer's recommended air pressure. For example, the low air pressure detection threshold Th2 is set to a value obtained by decreasing the manufacturer's recommended air pressure by a certain percentage (20%). This low air pressure detection threshold Th2 is used not for puncture but for a low air pressure alarm when air naturally leaks from the tire. When the tire air pressure falls below the low air pressure detection threshold Th2 stored in the memory 13, the CPU 11 warns the user that the air pressure has decreased through the indicator 15.

The initial value of the sudden pressure reduction detection threshold Th1 is set to the same value as the low air pressure detection threshold Th2. Then, the sudden pressure reduction detection threshold Th1 is updated as the tire air pressure increases.
Specifically, the tire air pressure increases according to the temperature of the tire according to Boyle Charles' law. For this reason, when the vehicle travels, the tire air pressure increases as the tire temperature rises due to frictional heat with the road. Therefore, when the vehicle starts running, the tire air pressure gradually increases, and after the vehicle stops, the increased air pressure decreases.

  When the CPU 11 receives the information signal, the CPU 11 determines whether or not the tire air pressure included in the signal exceeds the maximum value of the tire air pressure stored in the memory 13. From the above situation, it is considered that the tire air pressure exceeds the maximum value while the vehicle is running. When the CPU 11 determines that the tire air pressure included in the information signal exceeds the maximum value, the CPU 11 updates the sudden pressure reduction detection threshold Th1 to a value decreased by a certain ratio (for example, 20%) with respect to the air pressure. At this time, the CPU 11 updates the maximum value stored in the memory 13 to the tire air pressure included in the information signal received this time.

  Therefore, as indicated by the triangular mark in FIG. 2, the sudden pressure reduction detection threshold Th1 is updated when the tire air pressure reaches the maximum value as the vehicle travels. This sudden pressure reduction threshold value Th1 is used for an alarm when the tire is punctured.

  The CPU 11 recognizes that the sudden decompression bit is included in the information signal, and warns that the tire is punctured through the indicator 15 when the tire air pressure included in the signal is equal to or less than the sudden decompression detection threshold Th1. On the other hand, even if the tire air pressure included in the information signal is equal to or less than the sudden pressure reduction detection threshold Th1, the CPU 11 does not issue a warning unless the signal is included in the low pressure detection threshold Th2 unless the rapid pressure reduction bit is included in the signal. . In this example, the rapid pressure reduction detection threshold Th1 is set for each tire.

  Here, as described in the above “problem to be solved by the invention”, for example, the threshold value may not be an appropriate value due to a change in outside air temperature. Therefore, the sudden pressure reduction detection threshold Th1 is automatically initialized every time the air pressure adjustment is executed.

  Specifically, as shown in FIG. 3, when the air pressure change ΔP within the predetermined time T1 becomes equal to or higher than the predetermined pressure P1, the CPU 11 sets the sudden pressure reduction detection threshold Th1 as the low air pressure detection threshold Th2 as the air pressure adjustment is executed. The initial value is the same value as. Then, the maximum value of the air pressure stored in the memory 13 is reset. This completes the initialization process.

  Here, since it is expected that the air pressure adjustment is performed every one to two months, it is possible to set the sudden pressure reduction detection threshold Th1 corresponding to at least the season (exactly the outside air temperature). Thereby, the precision concerning the warning of sudden pressure reduction can be improved. Moreover, since the sudden pressure reduction detection threshold Th1 is automatically initialized when the air pressure is adjusted, the operation of the initialization switch is not necessary, and convenience is improved.

  Further, the low air pressure detection threshold Th2 is a fixed value that does not depend on the air pressure adjusted by the user. Therefore, the low air pressure detection threshold Th2 is prevented from being set outside the proper range, and a warning can be reliably issued when the tire air pressure falls below a certain level.

The first threshold corresponds to the sudden pressure reduction detection threshold Th1, and the second threshold corresponds to the low air pressure detection threshold Th2.
Hereinafter, the processing procedure of the CPU 11 at the time of updating the sudden pressure reduction detection threshold Th1 will be described with reference to the flowchart of FIG. The flowchart is repeatedly executed at a predetermined control cycle.

  First, an information signal is received (S101), and the tire air pressure included in the signal is recognized (S102). Then, it is determined whether or not the air pressure exceeds the maximum value of the tire air pressure stored in the memory 13 (S103). When it is determined that the maximum value is not exceeded (NO in S103), the process is terminated. That is, unless the tire air pressure exceeds the maximum value, the sudden pressure reduction detection threshold Th1 is not updated.

  On the other hand, when it is determined that the tire air pressure exceeds the maximum value (YES in S103), the rapid pressure reduction detection threshold Th1 is updated based on the air pressure (S104). The maximum value stored in the memory 13 is updated to the air pressure value of the information signal received this time (S105). The process is thus completed.

  Next, the procedure of the initialization process of the sudden pressure reduction detection threshold Th1 in the CPU 11 will be described with reference to FIG. The flowchart is repeatedly executed at a predetermined control cycle.

  First, it is determined whether or not air pressure adjustment has been performed (S201). When it is determined that the air pressure adjustment is not performed (NO in S201), the process is terminated. That is, the presence / absence of air pressure adjustment is monitored every predetermined control cycle. When it is determined that the air pressure adjustment has been executed (YES in S201), the sudden pressure reduction detection threshold Th1 stored in the memory 13 is set as an initial value, and the maximum value of the tire air pressure is reset (S202). The process is thus completed.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) The sudden pressure reduction threshold value Th1 is automatically updated from the initial value as the air pressure increases. When the tire air pressure adjustment is executed, the sudden pressure reduction detection threshold Th1 is initialized to the same initial value as the low air pressure detection threshold Th2. As a result, initialization is performed every time the tire air pressure is adjusted, and the sudden pressure reduction detection threshold Th1 corresponding to the pressure that changes with the outside air temperature can be automatically set.

  (2) Two threshold values are properly used as necessary. For example, when the tire is punctured, a warning is issued when the air pressure of the tire suddenly depressurizes and falls below the sudden depressurization detection threshold Th1. Therefore, a warning related to tire puncture can be promptly performed.

  Further, the low air pressure detection threshold Th2 is a fixed value. Therefore, it is not necessary to set the low air pressure detection threshold Th2 through the operation of the initialization switch after adjusting the air pressure to an appropriate value as in the prior art. Therefore, convenience is improved. Furthermore, since the initialization switch can be omitted, the TPMS can be configured more easily.

  Further, since the low air pressure detection threshold Th2 does not depend on the air pressure adjusted by the user, the low air pressure detection threshold Th2 is prevented from being set outside the appropriate range. Thereby, when the tire air pressure naturally leaks, a warning can be given at an appropriate timing.

  (3) When the tire air pressure exceeds the maximum value stored in the memory 13, the sudden pressure reduction detection threshold Th <b> 1 is updated to a value that is reduced by a certain percentage with respect to the air pressure. Thus, even when the air pressure increases due to the temperature rise of the tire, a warning can be reliably issued when the tire air pressure decreases by a certain rate.

  In particular, European legislation requires that a warning be issued when the air pressure of a tire is increased by 20% after the tire has been increased by running the vehicle for 20 minutes. According to the above configuration, a system suitable for this European law can be constructed.

(4) As described above, regardless of the air pressure after the air pressure adjustment, the sudden pressure reduction detection threshold Th1 is set to an initial value. Therefore, the initialization process can be executed without waiting for the completion of the air pressure adjustment.
In addition, the said embodiment can be implemented with the following forms which changed this suitably.

-You may abbreviate | omit the low air pressure detection threshold Th2 in the said embodiment. Even in this case, a warning is issued when the pressure is suddenly reduced through the sudden pressure reduction detection threshold Th1.
In the above embodiment, when the tire air pressure included in the information signal exceeds the maximum value stored in the memory 13, the sudden pressure reduction detection threshold Th1 is updated. However, the update timing of the sudden pressure reduction detection threshold Th1 is not limited to this, and may be updated when, for example, the average air pressure in the past certain period becomes maximum.

  In the above embodiment, it is determined that the air pressure adjustment has been performed when the change ΔP in the air pressure within the certain time T1 becomes equal to or greater than the certain pressure P1. However, when the air pressure change ΔP approximates zero after the air pressure change ΔP within the predetermined time T1 becomes equal to or greater than the constant pressure P1, the sudden pressure reduction detection threshold Th1 may be set as the initial value, assuming that the air pressure adjustment is completed. This makes it more accurate to determine whether or not air pressure adjustment has been performed.

  In the above embodiment, when it is recognized that the sudden decompression bit is added to the information signal, the sudden decompression occurs when the tire air pressure included in the signal is equal to or less than the sudden decompression detection threshold Th1. A warning is made. However, the CPU 11 of the vehicle 1 may determine whether or not sudden decompression has occurred based on the tire air pressure included in the information signal without relying on the sudden decompression bit. In this case, the CPU 11 determines that sudden pressure reduction has occurred when there has been a decrease over a certain pressure in a certain time based on the tire air pressure included in the continuously received information signal. Thereby, even if it is the structure where the sensor unit 30 does not transmit the information signal which added the rapid decompression bit, the said embodiment is applicable.

  In the above embodiment, the information signal is transmitted from the sensor unit 30 at regular intervals regardless of whether the vehicle is traveling. However, the sensor unit 30 may transmit the information signal to the receiver 10 only when the vehicle is traveling. In this case, for example, the sensor unit 30 includes an acceleration sensor that detects the presence or absence of rotation of the tire as an 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. Further, the sensor unit 30 may transmit an information signal in response to a request signal transmitted from the vehicle.

Next, the technical idea that can be grasped from the embodiment will be described together with the effects.
(A) The receiver for a tire pressure monitoring system according to any one of claims 1 to 3, wherein the initial value is set based on a manufacturer recommended pressure.

According to this configuration, the initial value of the first threshold value can be set to an appropriate value by setting the initial value based on the manufacturer recommended pressure.
(B) The receiver of the tire pressure monitoring system according to claim 2, wherein the second threshold value is set based on a manufacturer recommended pressure.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 10 ... Receiver, 30 ... Sensor unit, 33 ... Pressure sensor.

Claims (3)

In the receiver of the tire pressure monitoring system that issues a warning when the tire air pressure included in the information signal from the sensor unit attached to each tire falls below the first threshold,
The first threshold value is updated from an initial value in accordance with a change in air pressure due to a temperature change of the tire, and after the tire air pressure fluctuates more than a certain value within a certain time according to the air pressure adjustment, the first threshold value is changed. A receiver of the tire pressure monitoring system as the initial value. In the receiver of the tire pressure monitoring system according to claim 1,
In addition to the first threshold, a second threshold having the same value as the initial value is set as a fixed value,
When the air pressure suddenly decreases, a warning is given when the air pressure falls below the first threshold,
A receiver for a tire pressure monitoring system that issues a warning even when the tire pressure falls below the second threshold except when the pressure is suddenly reduced. In the receiver of the tire pressure monitoring system according to claim 1 or 2,
When the tire air pressure included in the information signal is the maximum value in the period from when the first threshold value was finally set to the initial value to the present time, the tire pressure is decreased by a certain percentage with respect to the maximum value. A receiver of the tire pressure monitoring system for updating the first threshold value to a predetermined value.

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