Tire pressure monitoring device, tire pressure monitoring method, and monitoring program

Abstract

The monitoring unit of a tire pressure monitoring device includes: an acquisition unit that acquires air pressure data of a plurality of tires mounted on a vehicle; a calculation unit that calculates, based on the air pressure data, a first representative value related to the air pressure of each tire within a first period and a second representative value related to the air pressure of each tire within a second period longer than the first period, and calculates a reduction degree of the first representative value with respect to the second representative value for each tire; and a determination unit that determines that there is a decrease in air pressure when the reduction degree of one tire is equal to or greater than a first threshold value and the reduction degrees of other tires different from the one tire are less than the first threshold value.

Description

Technical Field

[0001] The present disclosure relates to a tire pressure monitoring device, a tire pressure monitoring method, and a monitoring program. Background Art

[0002] Regarding a decrease in tire pressure, there are a sharp decrease represented by puncture or rupture, and a slow decrease called slow leak. For example, in Japanese Patent Laid-Open No. 2007-196999, a technique is proposed in which pressure history data on a daily basis is calculated and determined particularly for detecting the latter slow leak. Summary of the Invention

[0003] Problems to be Solved by the Invention

[0004] However, in the technique described in Japanese Patent Laid-Open No. 2007-196999, since slow leak is detected by one tire, there is sometimes a false determination that slow leak has occurred due to differences in the running conditions of the vehicle.

[0005] An object of the present disclosure is to provide a tire pressure monitoring device, a tire pressure monitoring method, and a monitoring program that can suppress false determination and detect slow leak.

[0006] Means for Solving the Problems

[0007] The tire pressure monitoring device of the present disclosure includes: an acquisition unit that acquires pressure data of a plurality of tires mounted on a vehicle; a calculation unit that calculates a first representative value related to the pressure of each tire in a first period and calculates a second representative value related to the pressure of each tire in a second period longer than the first period, and calculates a reduction degree of the first representative value with respect to the second representative value for each tire; and a determination unit that determines that there is a decrease in pressure when the reduction degree of one tire is equal to or more than a first threshold and the reduction degrees of other tires different from the one tire are less than the first threshold.

[0008] Regarding the tire pressure monitoring device of the present disclosure, when the acquisition unit acquires the air pressure data of each of a plurality of tires mounted on a vehicle, the calculation unit calculates the reduction degree of each tire based on a first representative value and a second representative value. Here, the first representative value is a representative value related to the air pressure of each tire within a first period, and the second representative value is a representative value related to the air pressure of each tire within a second period that is longer than the first period. Each representative value can be defined by any one of the average value, median value, and mode value of a plurality of air pressures with different acquisition timings. In addition, each representative value can also be any one of the absolute value of the air pressure, the relative value with respect to the reference air pressure, and the relative ratio with respect to the reference air pressure. In addition, the reduction degree can be either the decrease value of the first representative value with respect to the second representative value or the decrease rate. Moreover, in this tire pressure monitoring device, when the reduction degree of one tire is equal to or greater than a first threshold value and the reduction degrees of other tires different from the one tire are less than the first threshold value, it is determined that there is a decrease in air pressure.

[0009] According to this tire pressure monitoring device, when it is determined that the reduction degree obtained by comparing the first representative value calculated based on short-term air pressure data with the second representative value calculated based on long-term air pressure data is equal to or greater than the first threshold value, it is possible to detect slow air leakage based on the decrease in air pressure. However, in this tire pressure monitoring device, even if the reduction degree of one tire is equal to or greater than the first threshold value, the slow air leakage of the one tire is detected only when the reduction degrees of other tires are less than the first threshold value. Therefore, for example, in the case where the operating time of the vehicle is short and the temperature is low, and the air pressure of all tires decreases, slow air leakage is not detected. That is to say, according to this tire pressure monitoring device, it is possible to exclude the change in air pressure caused by the difference in the operating conditions of the vehicle from the determination of slow air leakage, thereby suppressing false determination.

[0010] Effects of the Invention

[0011] According to the present disclosure, it is possible to suppress false determination and detect slow air leakage. Brief Description of the Drawings

[0012] Figure 1 It is a schematic structural diagram of a vehicle according to the first embodiment.

[0013] Figure 2 It is a block diagram showing the hardware structure of the sensor unit according to the first embodiment.

[0014] Figure 3 It is a block diagram showing the hardware structure of the monitoring unit according to the first embodiment.

[0015] Figure 4 It is a block diagram showing the functional structure of the monitoring unit according to the first embodiment.

[0016] Figure 5It is a flowchart showing the process in the monitoring unit.

[0017] Figure 6 It is a diagram for explaining the comparison between the reduced value and the first threshold in the process of the monitoring unit.

[0018] Figure 7 It is a diagram for explaining the comparison between the difference between the upper and lower limits of the first average value and the second threshold in the process of the monitoring unit. Detailed implementation mode

[0019] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. In addition, for structural elements and processes that perform the same functions in terms of action and function, the same reference numerals may be given in all the drawings and repeated descriptions may be appropriately omitted.

[0020] [First Embodiment]

[0021] (Structure)

[0022] As Figure 1 shown, the tire pressure monitoring system 10 of the first embodiment is mounted on the vehicle V. The vehicle V of the present embodiment includes three axles Ax, namely the first axle Ax1, the second axle Ax2, and the third axle Ax3, from the front side of the vehicle, and a plurality of tires T are provided on each axle Ax. Specifically, the first axle Ax1 is provided with a tire T1 on the left side in the vehicle width direction and a tire T2 on the right side in the vehicle width direction, and the second axle Ax2 is provided with a tire T3 on the left side in the vehicle width direction and a tire T4 on the right side in the vehicle width direction. In addition, the third axle Ax3, which is the rear axle, is provided with a tire T5 and a tire T6 on the left side in the vehicle width direction, and a tire T7 and a tire T8 on the right side in the vehicle width direction.

[0023] The tire pressure monitoring system 10 of the present embodiment includes a sensor unit 12 mounted on each tire T and a monitoring unit 14 as a tire pressure monitoring device provided at the driver's seat of the vehicle V.

[0024] The sensor unit 12 is a device having a function of acquiring the air pressure data of the tire T and transmitting the air pressure data of the tire T to the monitoring unit 14. The sensor unit 12 can be a device installed inside the tire T such as on the wheel or the tire T, or a device provided outside the tire T such as on the tire valve.

[0025] As Figure 2 shown, the sensor unit 12 of the present embodiment is configured to include a control unit 20, an antenna 22, and a pressure sensor 24.

[0026] The control unit 20 is configured to include a CPU (Central Processing Unit), a ROM (ReadOnly Memory), a RAM (Random Access Memory), a communication device 20D, and an input / output I / F 20E. The CPU 20A, the ROM 20B, the RAM 20C, the communication device 20D, and the input / output I / F 20E are connected via an internal bus 20F so as to be able to communicate with each other.

[0027] The CPU 20A is a central arithmetic processing unit that reads a program from the ROM 20B and executes the program using the RAM 20C as a working area.

[0028] The ROM 20B stores various programs and various data. In the ROM 20B of the present embodiment, ID information 110 and a control program 100 for controlling the sensor unit 12 are stored. In the ID information 110, a terminal ID unique to the sensor unit 12 is stored to identify the tire T.

[0029] The RAM 20C temporarily stores programs or data as a working area.

[0030] The communication device 20D has a function of performing wireless communication with the monitoring unit 14. A known communication method can be applied. The communication device 20D in the sensor unit 12 only needs to have a sending function. The antenna 22 is connected to the communication device 20D.

[0031] The input / output I / F 20E is an interface for connecting to other devices constituting the sensor unit 12. The input / output I / F 20E of the sensor unit 12 is connected to a pressure sensor 24. In addition, the pressure sensor 24 may also be directly connected to the internal bus 20F. The pressure sensor 24 is a sensor using a known method.

[0032] In each sensor unit 12, the pressure sensor 24 detects the air pressure of the tire T on which the sensor unit 12 is mounted. Then, each sensor unit 12 assigns the terminal ID stored in the ID information 110 to the detected air pressure data and sends it to the monitoring unit 14.

[0033] The monitoring unit 14 is a device having a function of monitoring the air pressure of each tire T based on the air pressure data received from each sensor unit 12.

[0034] As Figure 3 shown, the monitoring unit 14 of the present embodiment is configured to include a control unit 20, an antenna 22, a monitor 26, and a speaker 28.

[0035] The structure of the control unit 20 in the monitoring unit 14 is the same as that of the control unit 20 in the sensor unit 12. However, a monitoring program 150 and a tire pressure DB (database) 160 are stored in the ROM 20B of the monitoring unit 14. The monitoring program 150 is used to control the monitoring unit 14, and the tire pressure DB (database) 160 stores data related to the tire pressure of each tire T.

[0036] The input / output I / F 20E of the monitoring unit 14 is connected to the monitor 26 and the speaker 28.

[0037] The monitor 26 is a display such as a liquid crystal display, and is configured so that the driver of the vehicle V can visually confirm it.

[0038] The speaker 28 is provided in a side-by-side manner with the monitor 26, and outputs sounds, alarm sounds, etc. to the driver of the vehicle V.

[0039] As Figure 4 shown, in the monitoring unit 14, the control unit 20 functions as an acquisition unit 200, a calculation unit 210, and a determination unit 220 by executing the monitoring program 150 stored in the ROM 20B by the CPU 20A.

[0040] The acquisition unit 200 has a function of acquiring the tire pressure data of a plurality of tires T mounted on the vehicle V. The acquisition unit 200 acquires the tire pressure data at a preset time interval. In addition, the monitoring unit 14 has correlation data between each tire T and the terminal ID. When receiving the tire pressure data from each sensor unit 12, the acquisition unit 200 acquires the tire pressure data of each tire T based on the terminal ID.

[0041] The calculation unit 210 has a function of calculating the average value of the tire pressures of each tire T based on the tire pressure data acquired by the acquisition unit 200. The calculation unit 210 calculates the average value of the tire pressures of each tire T in the first period, that is, the first average value. In addition, the calculation unit 210 calculates the average value of the tire pressures of each tire T in the second period, that is, the second average value. And the calculation unit 210 calculates the reduction value of the first average value relative to the second average value for each tire T, that is, the value obtained by subtracting the second average value from the first average value.

[0042] Here, the first period is the minimum unit for managing the operation of the vehicle V, and is set to 1 day, for example. In addition, the second period is a period longer than the first period, and is set to N days (N>2), for example. In addition, the first period and the second period do not necessarily need to be in units of days, and can also be set in units of hours. The first average value is an example of the first representative value, the second average value is an example of the second representative value, and the reduction value is an example of the degree of reduction.

[0043] In addition, whenever barometric pressure data is acquired in the acquisition unit 200, the calculation unit 210 updates the first average value for that day based on the new barometric pressure data. Additionally, whenever the date changes, the calculation unit 210 calculates the average of the first average values for N days as the second average value. Further, in the case where the first average values for N days are not stored in the barometric pressure DB 160, the average of the first average values for the number of stored days is calculated as the second average value.

[0044] The determination unit 220 has a function of determining a decrease in the air pressure of the tire T. For a decrease in air pressure, there is a sharp decrease such as a puncture and a slow decrease called a slow leak. The determination unit 220 determines that a puncture has occurred when the air pressure of the tire T is less than a preset limit value based on the currently acquired barometric pressure data.

[0045] In addition, for the tire T in which the decrease value calculated in the calculation unit 210 is equal to or greater than the first threshold value and satisfies a specified condition, the determination unit 220 determines that a slow leak has occurred. Here, the first threshold value is a threshold value set based on the actual situation when a slow leak occurred in the past.

[0046] The specified condition is a case where both (1) the decrease value of the other tire T on the same axle Ax as the tire T with a decrease value equal to or greater than the first threshold value is less than the first threshold value; and (2) the difference between the maximum value and the minimum value of the air pressure within the first period in the tire T with a decrease value equal to or greater than the first threshold value is equal to or less than the second threshold value are satisfied. The second threshold value is a threshold value set to be larger than the first threshold value in consideration of the increase in air pressure when air is filled into the tire T and the decrease in air pressure when the tire T is replaced (i.e., when the tire T is reassembled on the wheel).

[0047] (Flow of control)

[0048] Use Figure 5 the flowchart of Figure 6 and Figure 7 the graph of

[0049] In Figure 5 step S100 of

[0050] In step S101, the CPU 20A determines whether there is a tire T with a decrease value greater than or equal to the first threshold. When the CPU 20A determines that there is a tire T with a decrease value greater than or equal to the first threshold (i.e., when it is "Yes" in step S101), it proceeds to step S102. On the other hand, when the CPU 20A determines that there is no tire T with a decrease value greater than or equal to the first threshold (i.e., when it is "No" in step S101), it returns to step S100. For example, as Figure 6 shown, when the decrease value is less than the first threshold on the (N - 1)-th day, step S100 is repeated, but when the decrease value becomes greater than or equal to the first threshold on the N-th day, it proceeds to the next step S102.

[0051] In Figure 5 step S102, the CPU 20A determines whether there is a tire T with a decrease value less than the first threshold on the same axle Ax. When the CPU 20A determines that there is a tire T with a decrease value less than the first threshold on the same axle Ax (i.e., when it is "Yes" in step S102), it proceeds to step S103. On the other hand, when the CPU 20A determines that there is no tire T with a decrease value less than the first threshold on the same axle Ax (i.e., when it is "No" in step S102), it returns to step S100.

[0052] In step S103, the CPU 20A determines whether the difference between the upper and lower limits of the air pressure within the first period of the tire T with a decrease value exceeding the first threshold is less than or equal to the second threshold. When the CPU 20A determines that the difference between the upper and lower limits of the air pressure within the first period of the tire T with a decrease value exceeding the first threshold is less than or equal to the second threshold (i.e., when it is "Yes" in step S103), it proceeds to step S104. On the other hand, when the CPU 20A determines that the difference between the upper and lower limits of the air pressure within the first period of the tire T with a decrease value exceeding the first threshold is not less than or equal to the second threshold (i.e., when it is "No" in step S103), it proceeds to step S105.

[0053] For example, as Figure 7 shown, when the difference between the upper and lower limits of the air pressure within the first period exceeds the second threshold in the case of filling air into the tire T (represented by event X in Figure 7 ), it proceeds to step S105. Also, when the difference between the upper and lower limits of the air pressure within the first period exceeds the second threshold in the case of replacing the tire T (represented by event Y in Figure 7 ), it proceeds to step S105.

[0054] In Figure 5In step S104, CPU 20A determines that slow air leakage has occurred. Along with this, the monitoring unit 14 can notify the driver of the vehicle V of the occurrence of slow air leakage through the monitor 26, or notify the manager of the vehicle V of the occurrence of slow air leakage via a network (not shown). Then, the process returns to step S100.

[0055] In step S105, CPU 20A resets the second average value. Then, the process returns to step S100.

[0056] (Summary of the Embodiment)

[0057] As described above, in the monitoring unit 14 of the present embodiment, for the tire T in which the reduction value calculated in the calculation unit 210 is equal to or greater than the first threshold value and satisfies the specified conditions, the determination unit 220 determines that slow air leakage has occurred. As described above, the specified conditions are the cases where (1) the reduction values of the other tires T on the same axle Ax as the tire T with a reduction value equal to or greater than the first threshold value are less than the first threshold value; and (2) the difference between the maximum value and the minimum value of the air pressure within the first period in the tire T with a reduction value equal to or greater than the first threshold value is equal to or less than the second threshold value.

[0058] According to the present embodiment, when it is determined that the reduction value obtained by comparing the first average value calculated based on the short-term air pressure data with the second average value calculated based on the long-term air pressure is equal to or greater than the first threshold value, slow air leakage can be detected (see Figure 6 ). However, by setting the above (1) as the specified condition, even if the reduction value of one tire T is equal to or greater than the first threshold value, the slow air leakage of only that one tire T is detected only when the reduction values of the other tires T are less than the first threshold value. Therefore, for example, when the running time of the vehicle V is short and the temperature is low, and the air pressures of all the tires T on the same axle Ax decrease, slow air leakage is not detected. That is to say, according to the present embodiment, the change in air pressure due to the difference in the running conditions of the vehicle V can be excluded from the determination of slow air leakage, thereby suppressing misjudgment.

[0059] In addition, in the present embodiment, by setting the above (2) as the specified condition, the rapid change in air pressure in the short term such as filling air or replacing the tire T (see Figure 7 ) is excluded from the determination of slow air leakage. Thus, the misdetection of determining that slow air leakage has occurred for a tire T with normal air pressure can be suppressed.

[0060] Also, in the present embodiment, when determining slow air leakage of one tire T, the air pressure of other tires T mounted on the same axle Ax is referred to. For example, it can be said that the multiple tires T of the drive wheels are respectively in similar driving environments. According to the present embodiment, by comparing with the tires T in a similar driving environment for determination, it is possible to determine slow air leakage while reducing the influence of the external environment.

[0061] In addition, each parameter for determining slow air leakage, namely the first period, the second period, the first threshold, and the second threshold, can be changed and set according to the vehicle type, weight, and load of the vehicle V, as well as the type, size, and mounting position of the tire T. By changing the settings of each parameter, it is possible to detect slow air leakage at an early stage without degrading the detection accuracy of slow air leakage.

[0062] [Second Embodiment]

[0063] In the above-described embodiment, when determining slow air leakage of one tire T, the air pressure of other tires T mounted on the same axle Ax is referred to. In contrast, in the second embodiment, the air pressure of at least two or more tires mounted on the same axle Ax is referred to. Specifically, in the vehicle V of the present embodiment, four tires T are mounted on the third axle Ax3. For example, when determining slow air leakage of the tire T5, the air pressures of the tires T6, T7, and T8 can be referred to.

[0064] In this way, when determining slow air leakage, by using multiple other tires T for referring to the air pressure, even when the air pressures of multiple tires T decrease simultaneously, it is possible to determine slow air leakage while reducing the influence of the external environment.

[0065] [Third Embodiment]

[0066] Further, in the third embodiment, when determining slow air leakage of one tire T, the other tires T are configured such that their mounting positions on the left and right of the vehicle V are different from the mounting position of the one tire T on the left and right of the vehicle V. For example, on the third axle Ax3, when determining slow air leakage of the tire T5, the air pressure of the tire T8 is referred to.

[0067] In this way, when determining slow air leakage of one tire T, the air pressure of other tires T with different mounting positions on the left and right is referred to. According to the present embodiment, when determining slow air leakage, it is possible to exclude the influence of adjacent tires T (for example, the tire T6 in the above example) that may have their air pressures decrease simultaneously.

[0068] [Postscript]

[0069] In the above-described embodiments, the first average value is exemplified as the first representative value, and the second average value is exemplified as the second representative value, but it is not limited thereto. For example, the median value or the mode value of the air pressure of each tire T within the first period may be set as the first representative value. Additionally, for example, the median value or the mode value of the air pressure of each tire T within the second period may be set as the second representative value.

[0070] Furthermore, in the above-described embodiments, slow air leakage is detected by referring to the air pressure of the tires T provided on the same axle Ax, but slow air leakage may also be detected by referring to the air pressure of the tires T provided on different axles Ax. For example, when determining slow air leakage of the tire T on the third axle Ax3, the air pressure of the tire T on the first axle Ax1 and the air pressure of the tire on the second axle Ax2 can be referred to.

[0071] Moreover, the first average value and the second average value in the above-described embodiments are set as the absolute values of the air pressure, but it is not limited thereto, and either the relative value with respect to the reference air pressure or the relative ratio with respect to the reference air pressure may be used. By setting the first average value and the second average value as the relative ratio, slow air leakage can be detected by referring to the air pressure of tires T of different sizes. Additionally, the reduction value is set as the value obtained by subtracting the second average value from the first average value, but it may also be set as the rate of decrease of the first average value with respect to the second average value.

[0072] In the above-described embodiment, the first period is set as 1 day, and the second period is set as N days. In this case, when there is a non-driving day of the vehicle V within the N-day period, in order to ensure the air pressure data for the amount of N days, the starting date may be advanced by the amount of the non-driving days. For example, when the second period is 5 days and the air pressure on November 10th is monitored, generally, the second average value is calculated as the average value of November 6th, 7th, 8th, 9th, and 10th. However, when November 7th is a non-driving day of the vehicle V, in order to ensure the 5-day period, the average value of November 5th, 6th, 8th, 9th, and 10th can be calculated as the second average value.

[0073] In addition, various processes performed by the CPU 20A reading software (program) in the above-described embodiments can also be executed by various processors other than the CPU. Examples of the processors in this case include PLDs (Programmable Logic Devices) such as FPGAs (Field-Programmable Gate Arrays) that can change the circuit structure after manufacturing, and dedicated circuits such as ASICs (Application Specific Integrated Circuits) that have a circuit structure designed specifically for executing specific processes. In addition, the above-described processes can be executed by one of these various processors, or can be executed by a combination of two or more processors of the same type or different types (for example, a combination of multiple FPGAs, and a combination of a CPU and an FPGA). More specifically, the hardware configurations of these various processors are circuits formed by combining circuit elements such as semiconductor elements.

[0074] In addition, in the above-described embodiments, it has been described that each program is pre-stored (installed) in a computer-readable non-transitory recording medium. For example, the control program 100 of the sensor unit 12 is pre-stored in the ROM 20B, and the monitoring program 150 of the monitoring unit 14 is pre-stored in the ROM 20B. However, this is not limited thereto, and each program can also be provided in a manner of being recorded in a non-transitory recording medium such as a CD-ROM (Compact Disc Read Only Memory), a DVD-ROM (Digital Versatile Disc Read Only Memory), and a USB (Universal Serial Bus) memory. In addition, the program can also be configured to be downloaded from an external device via a network.

[0075] The flow of the processes described in the above-described embodiments is also an example, and unnecessary steps can be deleted, new steps can be added, or the order of processes can be changed within the scope not departing from the gist.

[0076] The entirety of the disclosure of Japanese Patent Application No. 2020-202900 filed on December 7, 2020 is incorporated herein by reference.

[0077] Regarding the incorporation by reference of each of the documents, patent applications, and technical standards described in this specification, they are incorporated herein by reference to the same extent as if specifically and individually described.

Claims

1. A tire pressure monitoring device, comprising: An acquisition unit that acquires air pressure data of a plurality of tires mounted on a vehicle; A calculation unit that calculates a first representative value related to the air pressure of each tire within a first period and calculates a second representative value related to the air pressure of each tire within a second period longer than the first period based on the air pressure data, and calculates the reduction degree of the first representative value relative to the second representative value for each tire; and A determination unit that determines that there is a decrease in air pressure when the reduction degree of one tire is equal to or greater than a first threshold value and the reduction degrees of other tires different from the one tire are less than the first threshold value.

2. The tire pressure monitoring device according to claim 1, wherein The determination unit determines that there is a decrease in air pressure when the reduction degree of the one tire is equal to or greater than the first threshold value, the reduction degrees of the other tires are less than the first threshold value, and the difference between the maximum value and the minimum value of the air pressure within the first period in the one tire is equal to or less than a second threshold value.

3. The tire pressure monitoring device according to claim 1 or 2, wherein The other tires and the one tire are mounted on the same axle.

4. The tire pressure monitoring device according to claim 1 or 2, wherein The reduction degree of the other tires is a representative value of the reduction degrees of two or more tires mounted on the same axle.

5. The tire pressure monitoring device according to claim 1 or 2, wherein The mounting positions of the other tires on the left and right of the vehicle are different from the mounting positions of the one tire on the left and right of the vehicle.

6. A tire pressure monitoring method in which a computer executes a process including the following processes: An acquisition process of periodically acquiring air pressure data of a plurality of tires mounted on a vehicle; A calculation process of calculating a first representative value related to the air pressure of each tire within a first period and calculating a second representative value related to the air pressure of each tire within a second period longer than the first period based on the air pressure data, and calculating the reduction degree of the first representative value relative to the second representative value for each tire; And A determination process of determining that there is a decrease in air pressure when the reduction degree of one tire is equal to or greater than a first threshold value and the reduction degrees of other tires different from the one tire are less than the first threshold value.

7. A monitoring program product including a monitoring program for causing a computer to execute a process including the following processes: An acquisition process of periodically acquiring air pressure data of a plurality of tires mounted on a vehicle; A calculation process of calculating a first representative value related to the air pressure of each tire within a first period and calculating a second representative value related to the air pressure of each tire within a second period longer than the first period based on the air pressure data, and calculating the reduction degree of the first representative value relative to the second representative value for each tire; And A determination process of determining that there is a decrease in air pressure when the reduction degree of one tire is equal to or greater than a first threshold value and the reduction degrees of other tires different from the one tire are less than the first threshold value.

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