Tire pressure reduction detection system, tire pressure reduction detection method, program

Abstract

To provide a tire pressure reduction detection system, a tire pressure reduction detection method, and a program that can suppress the decrease in accuracy of pressure reduction detection of pneumatic tires caused by changes in the type of pneumatic tire. [Solution] The tire pressure reduction determination system comprises: a first acquisition processing unit 51A that acquires the rotational speed of a tire mounted on a vehicle 1A; a second acquisition processing unit 54A that acquires the resonant frequency of the tire based on the acquired rotational speed; a replacement determination processing unit 58A that determines whether the difference between the acquired resonant frequency and a reference frequency exceeds a first determination value; and a change processing unit 59 that changes a threshold used in the pressure reduction determination process that determines whether the tire is depressurized or not when it is determined that the difference between the resonant frequency and the reference frequency exceeds the first determination value.

Description

Technical Field

[0001] The present disclosure relates to a tire pressure reduction determination system, a tire pressure reduction determination method, and a program.

Background Art

[0002] There is known a tire pressure reduction determination system capable of determining whether an inflated tire mounted on a vehicle is underinflated based on the rotational speed of the inflated tire. For example, there is known a tire pressure reduction determination system that acquires the resonance frequency of the inflated tire based on the rotational speed acquired during traveling of the vehicle, and determines that the inflated tire is underinflated when the acquired resonance frequency is less than a preset threshold value (see Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, in the vehicle, the type of the inflated tire may be changed by replacing the inflated tire. That is, the vehicle may be mounted with an inflated tire of a type different from the previous inflated tire. Here, in the tire pressure reduction determination system, if the same threshold value as before is used to perform the tire pressure reduction determination even after the type of the inflated tire is changed, the accuracy of the tire pressure reduction determination of the inflated tire decreases.

[0005] An object of the present disclosure is to provide a tire pressure reduction determination system, a tire pressure reduction determination method, and a program capable of suppressing a decrease in the accuracy of tire pressure reduction determination caused by a change in the type of an inflated tire.

Means for Solving the Problems

[0006] A tire pressure reduction determination system according to one aspect of the present disclosure comprises a first acquisition processing unit, a second acquisition processing unit, a determination processing unit, and a modification processing unit. The first acquisition processing unit acquires the rotational speed of a pneumatic tire mounted on a vehicle. The second acquisition processing unit acquires the resonant frequency of the pneumatic tire based on the rotational speed acquired by the first acquisition processing unit. The determination processing unit determines whether the difference between the resonant frequency acquired by the second acquisition processing unit and a preset reference frequency exceeds a preset first determination value. If the determination processing unit determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value, the modification processing unit changes the setting value used in the pressure reduction determination process that determines whether the pneumatic tire is depressurizing based on the rotational speed acquired by the first acquisition processing unit.

[0007] According to this tire pressure reduction detection system, by pre-setting the resonant frequency when the air pressure of the pneumatic tire is normal as the reference frequency, it is possible to detect the change and change the set value when the resonant frequency when the air pressure of the pneumatic tire is normal changes due to a change in the type of pneumatic tire. Therefore, it is possible to suppress the decrease in accuracy of the pneumatic tire pressure reduction detection caused by a change in the type of pneumatic tire. [Effects of the Invention]

[0008] According to this disclosure, it is possible to suppress the decrease in accuracy of pressure reduction detection of pneumatic tires caused by changes in the type of pneumatic tire. [Brief explanation of the drawing]

[0009] [Figure 1] Figure 1 shows the configuration of a tire pressure reduction determination system according to the first embodiment of this disclosure. [Figure 2] Figure 2 shows the configuration of a vehicle with a tire pressure reduction determination system according to the first embodiment of this disclosure. [Figure 3] Figure 3 shows the configuration of the server for the tire pressure reduction determination system according to the first embodiment of this disclosure. [Figure 4] Figure 4 is a flowchart showing an example of tire pressure monitoring processing performed in the tire pressure reduction determination system according to the first embodiment of this disclosure. [Figure 5] Figure 5 is a flowchart showing an example of a first threshold change process performed in the tire pressure reduction determination system according to the first embodiment of this disclosure. [Figure 6] Figure 6 shows the configuration of the tire pressure reduction determination system according to the second embodiment of this disclosure. [Figure 7] Figure 7 shows the configuration of a vehicle with a tire pressure reduction determination system according to the second embodiment of this disclosure. [Figure 8] Figure 8 is a flowchart showing an example of a second threshold change process performed in the tire pressure reduction determination system according to the second embodiment of this disclosure. [Modes for carrying out the invention]

[0010] The embodiments of this disclosure will be described below with reference to the attached drawings. Note that the following embodiments are merely examples of the embodiments of this disclosure and do not limit the technical scope of this disclosure.

[0011] [First Embodiment] First, with reference to Figure 1, the configuration of the tire pressure reduction determination system 100A according to the first embodiment of this disclosure will be described.

[0012] The tire pressure reduction detection system 100A can determine whether or not the pneumatic tire 10 (see Figure 1) (hereinafter referred to as "tire 10") mounted on the vehicle 1A (see Figure 1) is experiencing pressure reduction.

[0013] Here, in the tire pressure reduction determination system 100A, when the air pressure of the tire 10 drops by a predetermined reference pressure reduction amount from a predetermined optimum value, it is determined that the tire 10 is under pressure. For example, the reference pressure reduction amount is 20 percent of the optimum value.

[0014] As shown in FIG. 1, the tire pressure reduction determination system 100A includes a vehicle 1A and a server 2. In the tire pressure reduction determination system 100A, the vehicle 1A and the server 2 are communicably connected to each other via a communication network 3. For example, the communication network 3 is the Internet. Note that the tire pressure reduction determination system 100A of the present disclosure may be composed of only the vehicle 1A.

[0015] [Configuration of Vehicle 1A] Next, the configuration of the vehicle 1A will be described while referring to FIG. 2.

[0016] The vehicle 1A is an automobile such as a passenger car, a bus, and a truck. Note that the vehicle 1A is not limited to an automobile and may be a motorcycle, a three-wheeled passenger vehicle, or the like.

[0017] The vehicle 1A includes four tires 10 (see FIG. 1). Specifically, each of the tires 10 is an OE (Original Equipment) tire that is standardly mounted on the vehicle 1A.

[0018] In addition to each component necessary for traveling such as an engine, a plurality of wheels, the tires 10 (see FIG. 1) mounted on each of the wheels, a brake, and a steering mechanism, the vehicle 1A includes a control unit 11, an operation display unit 12, a communication unit 13, a storage unit 14, a GPS receiver 15, and a wheel speed sensor 16 shown in FIG. 2.

[0019] The control unit 11 comprehensively controls the vehicle 1A. As shown in FIG. 2, the control unit 11 includes a CPU 21, a ROM 22, and a RAM 23. The CPU 21 is a processor that executes various arithmetic processes. The ROM 22 is a non-volatile storage device in which information such as control programs for causing the CPU 21 to execute various processes is stored in advance. The RAM 23 is a volatile or non-volatile storage device used as a temporary storage memory (working area) for various processes executed by the CPU 21. The CPU 21 executes various control programs stored in advance in the ROM 22. Thereby, the CPU 21 comprehensively controls the vehicle 1A.

[0020] The operation display unit 12 includes a first display unit and a first operation unit. The first display unit displays various information according to a control instruction from the control unit 11. For example, the first display unit is a flat panel display such as a liquid crystal display. The first operation unit inputs various information to the control unit 11 according to a user's operation. For example, the first operation unit includes operation keys and a touch panel.

[0021] The communication unit 13 is a communication interface capable of performing data communication with an external device. Specifically, the communication unit 13 performs data communication with the server 2 via the communication network 3.

[0022] The storage unit 14 is a non-volatile storage device. For example, the storage unit 14 is a non-volatile memory such as a flash memory.

[0023] Map data of a predetermined specific area is stored in the storage unit 14. The map data is used for a search process of a driving route from the current position of the vehicle 1A to a destination set by a driver of the vehicle 1A or the like. The search process is executed by the control unit 11. The specific area may be an area including a plurality of countries, or may be any country, or may be an area included in any country.

[0024] The GPS receiver 15 is capable of receiving radio waves transmitted from GPS satellites. The control unit 11 can acquire vehicle position information indicating the current position of the vehicle 1A based on the information contained in the radio waves received by the GPS receiver 15.

[0025] The wheel speed sensor 16 is a sensor capable of detecting the rotational speed of the wheel (the rotational speed of the tire 10). A wheel speed sensor 16 is provided for each wheel. Each wheel speed sensor 16 outputs a wheel speed signal corresponding to the rotational speed of the wheel. The wheel speed signals output from each wheel speed sensor 16 are input to the control unit 11.

[0026] [Server 2 Configuration] Next, we will explain the configuration of Server 2, referring to Figure 3.

[0027] As shown in Figure 3, the server 2 comprises a control unit 31, an operation display unit 32, a communication unit 33, and a storage unit 34.

[0028] The control unit 31 comprehensively controls the server 2. As shown in Figure 3, the control unit 31 comprises a CPU 41, a ROM 42, and a RAM 43. The CPU 41 is a processor that performs various arithmetic operations. The ROM 42 is a non-volatile memory device in which information such as control programs for instructing the CPU 41 to perform various operations is pre-stored. The RAM 43 is a volatile or non-volatile memory device used as temporary storage memory (work area) for the various operations performed by the CPU 41. The CPU 41 executes the various control programs pre-stored in the ROM 42. In this way, the CPU 41 comprehensively controls the server 2.

[0029] The operation display unit 32 is the user interface of the server 2. The operation display unit 32 comprises a second display unit and a second operation unit. The second display unit displays various information in response to control instructions from the control unit 31. For example, the second display unit is a flat panel display such as a liquid crystal display. The second operation unit inputs various information to the control unit 31 in response to user operations. For example, the second operation unit includes a keyboard, mouse, and touch panel.

[0030] The communication unit 33 is a communication interface capable of performing data communication with external devices. Specifically, the communication unit 33 performs data communication with the vehicle 1A via the communication network 3.

[0031] The memory unit 34 is a non-volatile storage device. For example, the memory unit 34 is a storage device such as a non-volatile memory like flash memory, an SSD (solid state drive), or an HDD (hard disk drive).

[0032] [Configuration of the control unit 11] Next, with reference to Figure 2, the configuration of the control unit 11 of vehicle 1A will be described in more detail.

[0033] As shown in Figure 2, the control unit 11 includes a first acquisition processing unit 51A, a third acquisition processing unit 52, an appropriate determination processing unit 53, a second acquisition processing unit 54A, a pressure reduction determination processing unit 55, a notification processing unit 56, an update processing unit 57, a replacement determination processing unit 58A (an example of a determination processing unit of the present invention), and a change processing unit 59.

[0034] Specifically, the storage unit 14 of vehicle 1A has a tire pressure reduction determination program pre-stored in it, which causes the control unit 11 to function as one of the processing units shown in Figure 2. The CPU 21 of the control unit 11 functions as one of the processing units by executing the tire pressure reduction determination program.

[0035] Furthermore, some or all of the processing units included in the control unit 11 may be composed of electronic circuits. Also, the tire pressure reduction determination program may be a program that causes multiple processors to function as the processing units shown in Figure 2.

[0036] The first acquisition processing unit 51A acquires the rotational speed of the tire 10 mounted on the vehicle 1A.

[0037] For example, the first acquisition processing unit 51A acquires the rotational speed of the tire 10 each time a predetermined first determination timing occurs. For example, the first determination timing is a timing that occurs at a predetermined interval from the start of vehicle 1A's movement. For example, the interval is a time that can be arbitrarily set between 1 second and 10 minutes.

[0038] Furthermore, the first acquisition processing unit 51A acquires the rotation speed of the tire 10 when a predetermined specific operation is received. For example, the specific operation is a user operation on a specific button included in the operation display unit 12.

[0039] For example, the first acquisition processing unit 51A acquires the rotational speed of the tire 10 corresponding to the wheel speed sensor 16 based on the wheel speed signal output from the wheel speed sensor 16.

[0040] For example, when the first determination timing arrives, the first acquisition processing unit 51A continuously acquires the rotational speed of the tire 10 until a predetermined acquisition time has elapsed. That is, from the time the first determination timing arrives until the acquisition time has elapsed, the first acquisition processing unit 51A acquires the rotational speed of the tire 10 each time the wheel speed signal is output from the wheel speed sensor 16. For example, the acquisition time is 10 seconds. The rotational speeds of the multiple tires 10 acquired during the acquisition time are used to calculate the estimated resonant frequency of the tire 10.

[0041] Furthermore, when the specified operation is received, the first acquisition processing unit 51A continuously acquires the rotational speed of the tire 10 until a predetermined learning time has elapsed. For example, the learning time is a time that can be arbitrarily set between 30 minutes and 5 hours. The rotational speeds of the multiple tires 10 acquired during the learning time are used for learning the reference frequency, which will be described later.

[0042] The third acquisition processing unit 52 acquires driving condition information regarding the driving condition of the vehicle 1A when the first acquisition processing unit 51A acquires the rotational speed of the tire 10.

[0043] For example, the driving information includes speed information, speed change information, steering angle information, yaw rate information, road surface information, gradient information, and weather information. The speed information indicates the speed of the vehicle 1A. The speed change information indicates the acceleration or deceleration of the vehicle 1A. The steering angle information indicates the steering angle, which is the rotation angle of the steering wheel of the vehicle 1A. The yaw rate information indicates the yaw rate, which is the rotational angular velocity of the vehicle 1A around a vertical axis passing through the center of gravity of the vehicle 1A. The road surface information indicates the type of road surface on which the vehicle 1A is driving. The gradient information indicates the gradient of the road surface on which the vehicle 1A is driving. The weather information indicates the weather at the location where the vehicle 1A is driving.

[0044] For example, the third acquisition processing unit 52 acquires the speed information using a wheel speed sensor 16 corresponding to each of the wheels. The third acquisition processing unit 52 also acquires the speed change information based on the engine speed detection result by an engine speed sensor (not shown) and the presence or absence of a brake signal output when the brakes are pressed. The third acquisition processing unit 52 also acquires the steering angle information using a steering angle sensor (not shown) provided on the steering shaft of the steering wheel. The third acquisition processing unit 52 also acquires the yaw rate information using a yaw rate sensor (not shown). The third acquisition processing unit 52 also acquires the road surface information and gradient information based on the vehicle position information acquired using a GPS receiver 15 and the map data stored in the storage unit 14. The third acquisition processing unit 52 also acquires the weather information acquired by the weather observation system closest to the current position of the vehicle 1A from a website that provides such weather information.

[0045] The appropriateness determination processing unit 53 determines, based on the driving condition information acquired by the third acquisition processing unit 52, whether it is appropriate to acquire the resonant frequency of the tire 10 using the rotational speed of the tire 10 acquired by the first acquisition processing unit 51A.

[0046] For example, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotational speed of the tire 10 to obtain the resonant frequency of the tire 10 if the vehicle 1A's travel speed at the time of acquisition of the tire 10 by the first acquisition processing unit 51A does not fall within a predetermined speed range. For example, the speed range is between 50 kilometers per hour and 100 kilometers per hour.

[0047] Furthermore, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotational speed of the tire 10 to obtain the resonant frequency of the tire 10 if the acceleration of the vehicle 1A exceeds a predetermined value or the deceleration of the vehicle 1A exceeds a predetermined value when the rotational speed of the tire 10 is obtained by the first acquisition processing unit 51A.

[0048] Furthermore, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotational speed of the tire 10 to obtain the resonant frequency of the tire 10 if the steering angle at the time of acquisition of the rotational speed of the tire 10 by the first acquisition processing unit 51A is not included in a predetermined angular range centered on 0 degrees. For example, the angular range is between minus 5 degrees and 5 degrees.

[0049] Furthermore, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotational speed of the tire 10 to obtain the resonant frequency of the tire 10 if the yaw rate at the time of acquisition of the rotational speed of the tire 10 by the first acquisition processing unit 51A exceeds a predetermined value.

[0050] Furthermore, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotation speed to obtain the resonant frequency of the tire 10 when the vehicle 1A is traveling on a predetermined specific road surface different from a paved road surface when the first acquisition processing unit 51A is acquiring the rotation speed of the tire 10.

[0051] Furthermore, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotation speed of the tire 10 to obtain the resonant frequency of the tire 10 if the vehicle 1A is traveling on a road surface with a gradient exceeding a predetermined upper limit angle when the first acquisition processing unit 51A acquires the rotation speed of the tire 10. For example, the upper limit angle is 5 degrees.

[0052] Furthermore, the appropriateness determination processing unit 53 determines that it is inappropriate to use the rotation speed to obtain the resonant frequency of the tire 10 when the vehicle 1A is traveling in a rainy or snowy area and the amount of rainfall or snowfall exceeds a predetermined value.

[0053] Furthermore, the appropriateness determination processing unit 53 determines that it is appropriate to acquire the resonant frequency of the tire 10 using the rotational speed of the tire 10 acquired by the first acquisition processing unit 51A if it is not determined to be inappropriate based on the speed information, speed change information, steering angle information, yaw rate information, road surface information, gradient information, and weather information.

[0054] The second data acquisition unit 54A acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired by the first data acquisition unit 51A.

[0055] Here, the second acquisition processing unit 54A acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired by the first acquisition processing unit 51A, which is determined to be appropriate based on the driving condition information acquired by the third acquisition processing unit 52. This makes it possible to avoid acquiring the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired under driving conditions that are not suitable for acquiring the resonant frequency of the tire 10.

[0056] For example, each time the first determination timing arrives, the second acquisition processing unit 54A acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired in response to the arrival of the first determination timing. Specifically, the second acquisition processing unit 54A acquires the resonant frequency of the tire 10 based on the rotational speeds of multiple tires 10 acquired during the acquisition time.

[0057] Furthermore, when the specific operation is received, the second acquisition processing unit 54A acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired in response to the acceptance of the specific operation. Specifically, the second acquisition processing unit 54A acquires the resonant frequencies of multiple tires 10 based on the rotational speeds of multiple tires 10 acquired during the learning time.

[0058] The method used by the second data acquisition unit 54A to acquire the resonant frequency of the tire 10 may be a known method. For example, the second data acquisition unit 54A can calculate an estimated resonant frequency of the tire 10 by performing a time-series analysis of rotational acceleration information calculated from the rotational speed of the tire 10 acquired by the first data acquisition unit 51A, based on a second-order autoregressive (AR) model.

[0059] Incidentally, the resonant frequency of tire 10 may change depending on the driving speed of vehicle 1A. In response to this, vehicle 1A corrects the acquired resonant frequency of tire 10 based on the driving speed of vehicle 1A.

[0060] For example, the memory unit 14 has a relational expression pre-stored that shows the relationship between the driving speed of vehicle 1A and the correction value of the resonant frequency of tire 10. The relational expression is defined so that the correction value becomes zero when the driving speed of vehicle 1A is a predetermined reference speed. For example, the relational expression is a linear function. The relational expression can be obtained by conducting an experiment using an experimental vehicle equipped with the OE tire to investigate the relationship between the driving speed of the experimental vehicle and the resonant frequency of the OE tire. The experimental vehicle is the same type of vehicle as vehicle 1A.

[0061] Then, the second acquisition processing unit 54A obtains the correction value by substituting the vehicle 1A's driving speed at the time of acquiring the tire 10's resonant frequency into the relational expression, and corrects the tire 10's resonant frequency by adding the acquired correction value to the tire 10's resonant frequency.

[0062] The pressure reduction determination processing unit 55 performs a pressure reduction determination process to determine whether or not the tire 10 is experiencing pressure reduction, based on the rotational speed of the tire 10 acquired by the first acquisition processing unit 51A.

[0063] Specifically, in the pressure reduction determination process, if the difference between the resonant frequency based on the rotational speed of the tire 10 acquired by the first acquisition processing unit 51A, that is, the resonant frequency of the tire 10 acquired by the second acquisition processing unit 54A, and a preset reference frequency exceeds a preset threshold, it is determined that the tire 10 is experiencing pressure reduction.

[0064] Here, the reference frequency is the resonant frequency of the tire 10 when the air pressure of the tire 10 is the optimal value. The reference frequency is updated by the update processing unit 57. The initial value of the reference frequency is the initial frequency of the OE tire. The initial frequency of the OE tire is the resonant frequency of the OE tire when the air pressure of a new OE tire is the optimal value.

[0065] Here, we will explain the method for calculating the threshold.

[0066] The threshold is calculated based on the results of an experiment using the experimental vehicle to investigate the pressure reduction sensitivity of the OE tire. Here, the pressure reduction sensitivity of the OE tire is a value that indicates the amount of decrease in the resonant frequency of the OE tire when the air pressure of the OE tire decreases by a unit amount (for example, 1 percent of the optimal value).

[0067] Specifically, the threshold is calculated by multiplying the pressure reduction sensitivity of the OE tire by the reference pressure reduction amount.

[0068] For example, in vehicle 1A, the pre-calculated threshold is stored in the first storage area 61 of the storage unit 14 (see Figure 2).

[0069] The pressure reduction determination processing unit 55 executes the pressure reduction determination process using the threshold value stored in the first memory area 61.

[0070] The notification processing unit 56 notifies the user if it determines that the tire 10 is under pressure as a result of the pressure reduction determination process.

[0071] For example, the notification processing unit 56 causes the operation display unit 12 to display a message that indicates the presence of a tire 10 experiencing depressurization and the location of the tire 10 experiencing depressurization.

[0072] Furthermore, the notification processing unit 56 may count down a count value with a lower limit of zero if it is determined by the pressure reduction determination process that the tire 10 is not depressurized, and may count up the count value if it is determined by the pressure reduction determination process that the tire 10 is depressurized. The notification processing unit 56 may also notify that the tire 10 is depressurized when the count value reaches a predetermined value.

[0073] The update processing unit 57 updates the reference frequency based on the resonant frequency of the tire 10 acquired in response to the acceptance of the specific operation.

[0074] The aforementioned reference frequency is updated when the air pressure of the tire 10 is adjusted or when the tire 10 is replaced. In other words, in vehicle 1A, the specific operation is performed by the driver of vehicle 1A when the air pressure of the tire 10 is adjusted or when the tire 10 is replaced.

[0075] For example, when the resonant frequencies of multiple tires 10 are acquired in response to the acceptance of the specific operation, the update processing unit 57 stores the average value of the acquired resonant frequencies of the multiple tires 10 as the new reference frequency in the second storage area 62 of the storage unit 14. In other words, the control unit 11 learns the reference frequency based on the resonant frequencies of multiple tires 10 acquired in response to the acceptance of the specific operation.

[0076] By the way, in vehicle 1A, the type of tire 10 may change when the tire 10 is replaced. In other words, vehicle 1A may be fitted with a tire 10 (replacement tire) of a different type than the previous tire 10 (the aforementioned OE tire).

[0077] In this case, if the tire pressure reduction determination system 100A uses the same threshold value as before to determine the pressure of the tire 10 even after the type of tire 10 has been changed, the accuracy of the tire pressure reduction determination will decrease. This is because the pressure reduction sensitivity used to calculate the threshold value differs for each type of tire 10.

[0078] In contrast, the tire pressure reduction determination system 100A according to the embodiment of this disclosure can suppress the decrease in accuracy of tire pressure reduction determination caused by a change in the type of tire 10, as described below.

[0079] The replacement determination processing unit 58A determines whether the difference between the resonant frequency of the tire 10 acquired by the second acquisition processing unit 54A and the reference frequency exceeds a preset first determination value.

[0080] For example, the first determination value is set to a value greater than the variation in the initial frequency of the multiple OE tires.

[0081] For example, when the specific operation is received, the replacement determination processing unit 58A determines whether the difference between the reference frequency after updating by the update processing unit 57 and the reference frequency before updating exceeds the first determination value.

[0082] The first determination value may also be a value obtained by multiplying the reference frequency by a predetermined percentage (for example, 5 percent).

[0083] The modification processing unit 59 modifies the threshold value (an example of a setting value in the present invention) used in the pressure reduction determination process when the replacement determination processing unit 58A determines that the difference between the resonant frequency of the tire 10 and the reference frequency exceeds the first determination value.

[0084] For example, if the replacement determination processing unit 58A determines that the difference between the resonant frequency of the tire 10 and the reference frequency exceeds the first determination value, the change processing unit 59 changes the threshold value to a value based on the maximum pressure reduction sensitivity among a plurality of pressure reduction sensitivities corresponding to a plurality of tire types.

[0085] For example, the storage unit 34 of server 2 is provided with a threshold storage unit 63, as shown in Figure 3.

[0086] The threshold value storage unit 63 stores multiple threshold values ​​corresponding to multiple tire types. The pressure reduction sensitivity corresponding to each tire type can be obtained by preparing multiple tires of the same size as the OE tire but of different tire types, and conducting an experiment to investigate the resonance frequency (initial frequency) when the tire is mounted on a vehicle of the same type as vehicle 1A and the air pressure is at the optimal value, and the resonance frequency when the air pressure is at an abnormal value (for example, 80 percent of the optimal value). Furthermore, the threshold value corresponding to each tire type can be calculated based on the pressure reduction sensitivity corresponding to each tire type and the reference pressure reduction amount.

[0087] The change processing unit 59 obtains the largest of the multiple thresholds corresponding to the multiple tire types stored in the threshold storage unit 63 of the server 2.

[0088] The change processing unit 59 then stores the threshold value obtained from the threshold value storage unit 63 as the new threshold value in the first storage area 61 of the storage unit 14.

[0089] Furthermore, if the replacement determination processing unit 58A determines that the difference between the resonant frequency of the tire 10 and the reference frequency exceeds the first determination value, the change processing unit 59 may set the average value of the multiple threshold values ​​corresponding to the multiple tire types as the new threshold value.

[0090] [Tire pressure monitoring process] The following describes an example of the procedure for tire pressure monitoring performed by the control unit 11 of vehicle 1A, with reference to Figure 4. Here, steps S11, S12, etc., represent the numbers of the processing steps performed by the control unit 11. The tire pressure monitoring procedure is performed while vehicle 1A is in motion. Furthermore, the tire pressure monitoring procedure is performed for each tire 10.

[0091] <Step S11> First, in step S11, the control unit 11 determines whether or not the first determination timing has arrived.

[0092] Here, if the control unit 11 determines that the first determination timing has arrived (Yes side of S11), it proceeds to step S12. If the first determination timing has not arrived (No side of S11), the control unit 11 waits for the arrival of the first determination timing in step S11.

[0093] <Step S12> In step S12, the control unit 11 acquires the rotational speed of the tire 10. The processes in steps S11 and S12 are performed by the first acquisition processing unit 51A of the control unit 11.

[0094] Specifically, the control unit 11 acquires the rotational speed of the tire 10 using the wheel speed sensor 16. The control unit 11 also continuously acquires the rotational speed of the tire 10 until the acquisition time has elapsed.

[0095] <Step S13> In step S13, the control unit 11 acquires the driving status information. The processing in step S13 is performed by the third acquisition processing unit 52 of the control unit 11.

[0096] Specifically, the control unit 11 acquires the speed information using the wheel speed sensor 16 corresponding to each of the wheels. The control unit 11 also acquires the speed change information based on the engine speed detection result by the engine speed sensor and the presence or absence of the brake signal output. The control unit 11 also acquires the steering angle information using the steering angle sensor. The control unit 11 also acquires the yaw rate information using the yaw rate sensor. The control unit 11 also acquires the road surface information and gradient information based on the vehicle position information acquired using the GPS receiver 15 and the map data stored in the storage unit 14. The control unit 11 also acquires the weather information acquired by the weather observation system closest to the current position of the vehicle 1A from the website.

[0097] <Step S14> In step S14, the control unit 11 determines, based on the driving condition information obtained in step S13, whether it is appropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12. The process in step S14 is performed by the appropriateness determination processing unit 53 of the control unit 11.

[0098] Specifically, if the speed information obtained in step S13 indicates a speed outside the speed range, the control unit 11 determines that it is inappropriate to use the rotational speed of the tire 10 obtained in step S12 to obtain the resonant frequency of the tire 10.

[0099] Furthermore, if the control unit 11 determines, based on the speed change information obtained in step S13, that the acceleration of the vehicle 1A exceeds a predetermined value, or that the deceleration of the vehicle 1A exceeds a predetermined value, it determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0100] Furthermore, if the steering angle information obtained in step S13 indicates an angle outside the angle range, the control unit 11 determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0101] Furthermore, if the control unit 11 determines that the yaw rate exceeds a predetermined value based on the yaw rate information obtained in step S13, it determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0102] Furthermore, if the road surface information obtained in step S13 indicates the specific road surface, the control unit 11 determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0103] Furthermore, if the gradient information obtained in step S13 indicates an angle greater than the upper limit angle, the control unit 11 determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0104] Furthermore, if the weather information obtained in step S13 indicates rain or snow, and the amount of rainfall or snowfall exceeds a predetermined value, the control unit 11 determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0105] Furthermore, if the control unit 11 does not determine that it is inappropriate based on the driving condition information obtained in step S13, it determines that it is inappropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12.

[0106] Here, if the control unit 11 determines that it is appropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12 (Yes side of S14), it proceeds to step S15. If it is not appropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S12 (No side of S14), the control unit 11 proceeds to step S12.

[0107] <Step S15> In step S15, the control unit 11 acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired in the preceding step S12. The processing in step S15 is performed by the second acquisition processing unit 54A of the control unit 11.

[0108] Specifically, the control unit 11 calculates an estimated resonant frequency of the tire 10 by performing a time-series analysis of rotational acceleration information calculated from the rotational speed of the tire 10 obtained in the previous step S12, based on a second-order autoregressive (AR) model.

[0109] Furthermore, the control unit 11 obtains the correction value by substituting the vehicle speed 1A obtained in step S13 into the relational expression, and corrects the resonant frequency of the tire 10 by adding the obtained correction value to the resonant frequency of the tire 10.

[0110] <Step S16> In step S16, the control unit 11 determines whether the difference between the resonant frequency of the tire 10 obtained in step S15 and the reference frequency stored in the second storage area 62 of the storage unit 14 exceeds the threshold value stored in the first storage area 61 of the storage unit 14. The processing in step S16 is performed by the pressure reduction determination processing unit 55 of the control unit 11.

[0111] Here, if the control unit 11 determines that the difference between the resonant frequency of the tire 10 obtained in step S15 and the reference frequency exceeds the threshold (Yes side of S16), it proceeds to step S17. If the difference between the resonant frequency of the tire 10 obtained in step S15 and the reference frequency does not exceed the threshold (No side of S16), the control unit 11 proceeds to step S11.

[0112] <Step S17> In step S17, the control unit 11 notifies that the tire pressure 10 is decreasing. The processing in step S17 is performed by the notification processing unit 56 of the control unit 11.

[0113] Specifically, the control unit 11 causes the operation display unit 12 to display a message that includes information indicating the presence of a tire 10 that is losing pressure and the location of the tire 10 that is losing pressure.

[0114] [First threshold change process] Next, with reference to Figure 5, the tire pressure reduction determination method of this disclosure will be described along with an example of the procedure for the first threshold change process executed by the control unit 11 of the vehicle 1A. Note that the first threshold change process is executed while the vehicle 1A is running. Furthermore, the first threshold change process is executed for each tire 10.

[0115] <Step S21> First, in step S21, the control unit 11 determines whether or not the specific operation has been received.

[0116] Specifically, the control unit 11 determines that a specific operation has been received when it receives a user operation on the specific button included in the operation display unit 12.

[0117] If the control unit 11 determines that it has received the specific operation (Yes side of S21), it proceeds to step S22. If it has not received the specific operation (No side of S21), the control unit 11 waits for the specific operation to be received in step S21.

[0118] <Step S22> In step S22, the control unit 11 acquires the rotational speed of the tire 10. The processing in steps S21 and S22 is an example of the first acquisition step of this disclosure and is performed by the first acquisition processing unit 51A of the control unit 11.

[0119] Specifically, the control unit 11 continuously acquires the rotation speed of the tire 10 until the learning time has elapsed.

[0120] <Step S23> In step S23, the control unit 11 acquires the driving condition information. For example, the control unit 11 acquires the driving condition information for each divided period obtained by dividing the period for acquiring the rotational speed of the tire 10 by the processing in step S22 into equal intervals. The processing in step S23 is performed by the third acquisition processing unit 52 of the control unit 11.

[0121] <Step S24> In step S24, the control unit 11 determines, based on the driving condition information obtained in step S23, whether it is appropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained in step S22. For example, for each divided period, the control unit 11 determines, based on the driving condition information obtained during that divided period, whether it is appropriate to obtain the resonant frequency of the tire 10 using the rotational speed of the tire 10 obtained during that divided period. The processing in step S24 is performed by the appropriateness determination processing unit 53 of the control unit 11.

[0122] <Step S25> In step S25, the control unit 11 acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired in step S22. For example, for each of the division periods in which it is determined by the processing in step S24 that it is appropriate to acquire the resonant frequency of the tire 10, the control unit 11 acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired during that division period. The processing in step S25 is an example of the second acquisition step of this disclosure and is performed by the second acquisition processing unit 54A of the control unit 11.

[0123] <Step S26> In step S26, the control unit 11 updates the reference frequency. The process in step S26 is performed by the update processing unit 57 of the control unit 11.

[0124] For example, the control unit 11 stores the average of the resonant frequencies of the multiple tires 10 obtained in step S25 as the new reference frequency in the second storage area 62 of the storage unit 14.

[0125] <Step S27> In step S27, the control unit 11 determines whether the difference between the reference frequency after updating by the process in step S26 and the reference frequency before updating exceeds the first determination value. The process in step S27 is an example of the determination steps of this disclosure and is performed by the replacement determination processing unit 58A of the control unit 11.

[0126] Here, if the control unit 11 determines that the difference between the updated reference frequency and the reference frequency before the update exceeds the first determination value (Yes side of S27), it moves the process to step S28. If the difference between the updated reference frequency and the reference frequency before the update does not exceed the first determination value (No side of S27), the control unit 11 moves the process to step S21.

[0127] <Step S28> In step S28, the control unit 11 obtains the largest of the multiple thresholds corresponding to the multiple tire types stored in the threshold storage unit 63 of the server 2.

[0128] <Step S29> In step S29, the control unit 11 changes the threshold value. The processing in steps S28 and S29 is an example of the modification steps of the present disclosure and is performed by the modification processing unit 59 of the control unit 11.

[0129] Specifically, the control unit 11 stores the threshold obtained in step S28 as the new threshold in the first storage area 61 of the storage unit 14.

[0130] Thus, in the tire pressure reduction determination system 100A, the threshold used in the pressure reduction determination process is changed when the difference between the resonant frequency of the tire 10 acquired by the second acquisition processing unit 54A and the reference frequency exceeds the first determination value. By setting the resonant frequency when the tire 10 has normal air pressure as the reference frequency in advance, it is possible to detect the change and change the threshold when the resonant frequency when the tire 10 has normal air pressure changes due to a change in the type of tire 10. Therefore, it is possible to suppress a decrease in the accuracy of tire pressure reduction determination caused by a change in the type of tire 10.

[0131] [Second Embodiment] The configuration of the tire pressure reduction determination system 100B according to the second embodiment of this disclosure will be described below with reference to Figures 6 and 7.

[0132] As shown in Figures 1 and 6, the tire pressure reduction detection system 100B includes the same configuration as the tire pressure reduction detection system 100A, except that it includes vehicle 1B instead of vehicle 1A. Below, only the configuration of the tire pressure reduction detection system 100B that differs from that of the tire pressure reduction detection system 100A will be described.

[0133] As shown in Figures 2 and 7, vehicle 1B has the same configuration as vehicle 1A, except that it is equipped with a first acquisition processing unit 51B, a second acquisition processing unit 54B, and a replacement determination processing unit 58B instead of a first acquisition processing unit 51A, a second acquisition processing unit 54A, and a replacement determination processing unit 58A.

[0134] The first acquisition processing unit 51B acquires the rotational speed of the tire 10 each time the first determination timing arrives.

[0135] Furthermore, the first acquisition processing unit 51B acquires the rotational speed of the tire 10 each time a predetermined second determination timing (an example of an acquisition timing in this disclosure) occurs. For example, the second determination timing is a timing that occurs each time a specific amount of time has elapsed since the start of vehicle 1A's driving. The specific amount of time is the same as or longer than the learning time.

[0136] The second acquisition processing unit 54B acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired in response to the arrival of the first determination timing, each time the first determination timing occurs.

[0137] Furthermore, each time the second determination timing arrives, the second acquisition processing unit 54B acquires the resonant frequency of the tire 10 based on the rotational speed of the tire 10 acquired in response to the arrival of the second determination timing.

[0138] The replacement determination processing unit 58B determines whether the difference between the last acquired resonant frequency of the tire 10 and the reference frequency exceeds the first determination value when the resonant frequency of the tire 10 acquired by the second acquisition processing unit 54B at each second determination timing increases beyond a preset second determination value, or decreases beyond a preset third determination value.

[0139] For example, the second determination value is 10 percent of the threshold. Also, the third determination value is 50 percent of the threshold.

[0140] In vehicle 1B, the second threshold change process shown in Figure 8 is executed instead of the first threshold change process.

[0141] [Second threshold change process] The following describes an example of the procedure for the second threshold change process performed by the control unit 11 of vehicle 1B, with reference to Figure 8. Note that the second threshold change process is performed while vehicle 1B is in motion. Furthermore, the second threshold change process is performed for each tire 10.

[0142] As shown in Figures 5 and 8, the second threshold change process includes the same processing content as the first threshold change process, except that the processing of step S31 is performed instead of the processing of step S21, and the processing of step S32 is performed after the processing of step S25.

[0143] <Step S31> In step S31, the control unit 11 determines whether or not the second determination timing has arrived.

[0144] Here, if the control unit 11 determines that the second determination timing has arrived (Yes side of S31), it proceeds to step S22. If the second determination timing has not arrived (No side of S31), the control unit 11 waits for the second determination timing to arrive in step S31.

[0145] <Step S32> In step S32, the control unit 11 determines whether or not the predetermined determination conditions are met.

[0146] Specifically, the control unit 11 determines that the determination condition is satisfied if the average value of the resonant frequencies of the multiple tires 10 obtained in the processing of the immediately preceding step S25 increases by more than the second determination value compared to the previous time. Also, the control unit 11 determines that the determination condition is satisfied if the average value of the resonant frequencies of the multiple tires 10 obtained in the processing of the immediately preceding step S25 decreases by more than the third determination value compared to the previous time.

[0147] If the control unit 11 determines that the determination condition is met (Yes side of S32), it proceeds to step S26. If the determination condition is not met (No side of S32), the control unit 11 proceeds to step S31.

[0148] Thus, in the tire pressure reduction determination system 100B, when the resonant frequency of the tire 10 acquired at each second determination timing increases beyond the second determination value, or decreases beyond the third determination value, it is determined whether the difference between the last acquired resonant frequency of the tire 10 (the updated reference frequency) and the reference frequency before the update exceeds the first determination value. This makes it possible to automatically determine whether the threshold needs to be changed when the resonant frequency of the tire 10 increases due to air injection into the tire 10 or replacement of the tire 10. It also makes it possible to automatically determine whether the threshold needs to be changed when the resonant frequency of the tire 10 decreases significantly due to replacement of the tire 10. Therefore, compared to the configuration of the tire pressure reduction determination system 100A, which determines whether the threshold needs to be changed when the specific operation is accepted, it is possible to reduce the effort required to perform the specific operation.

[0149] The pressure reduction determination process may also be a process that determines that the tire 10 is experiencing pressure reduction when the resonant frequency of the tire 10 acquired by the second acquisition processing unit 54A is less than a specific value. Specifically, the specific value is the value obtained by subtracting the threshold from the reference frequency.

[0150] In this case, the modification processing unit 59 only needs to change the specific value used in the pressure reduction determination process (another example of the setting value of the present invention) when the replacement determination processing unit 58A determines that the difference between the resonant frequency of the tire 10 and the reference frequency exceeds the first determination value.

[0151] Furthermore, the modification processing unit 59 may change the slope of the relational expression used to correct the resonant frequency of the tire 10 (another example of the setting value in the present invention) along with the threshold value.

[0152] For example, the threshold storage unit 63 may store in advance combinations of the threshold value and the inclination corresponding to each of the tire types. The modification processing unit 59 then retrieves the maximum threshold value and the corresponding inclination from the threshold storage unit 63, and modifies the relational expression using the retrieved inclination. The relational expression may also be calculated based on various data such as the rotational speed of the tire 10 acquired while the vehicle 1A (or vehicle 1B) is in motion.

[0153] Furthermore, some of the processing units included in the control unit 11 may be provided in the control unit 31 of the server 2.

[0154] The threshold value storage unit 63 may also be provided in the storage unit 14 of the vehicle 1A.

[0155] The embodiments of this disclosure described above include the following disclosures (1) to (7).

[0156] Disclosure item (1) is a tire pressure reduction determination system comprising: a first acquisition processing unit for acquiring the rotational speed of a pneumatic tire mounted on a vehicle; a second acquisition processing unit for acquiring the resonant frequency of the pneumatic tire based on the rotational speed acquired by the first acquisition processing unit; a determination processing unit for determining whether the difference between the resonant frequency acquired by the second acquisition processing unit and a preset reference frequency exceeds a preset first determination value; and a change processing unit for changing a setting value used in a pressure reduction determination process for determining whether the pneumatic tire is depressurized based on the rotational speed acquired by the first acquisition processing unit when the determination processing unit determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value.

[0157] According to this system, by pre-setting the resonant frequency when the air pressure of the pneumatic tire is normal as the reference frequency, it is possible to detect the change and change the set value when the resonant frequency when the air pressure of the pneumatic tire is normal changes due to a change in the type of pneumatic tire. Therefore, it is possible to suppress the decrease in accuracy of the pressure reduction judgment of the pneumatic tire caused by a change in the type of pneumatic tire.

[0158] Disclosure item (2) is the tire pressure reduction determination system described in disclosure item (1), wherein the first acquisition processing unit acquires the rotation speed when at least a predetermined specific operation is received, the second acquisition processing unit acquires the resonant frequency based on the rotation speed acquired in response to the acceptance of the specific operation when the specific operation is received, and the tire pressure reduction determination system includes an update processing unit that updates the reference frequency based on the resonant frequency acquired in response to the acceptance of the specific operation, and the determination processing unit determines whether the difference between the reference frequency after updating by the update processing unit and the reference frequency before updating exceeds the first determination value when the specific operation is received.

[0159] According to this system, it is possible to determine whether or not the type of pneumatic tire has been changed at the timing of updating the reference frequency corresponding to the specific operation.

[0160] Disclosure item (3) is the tire pressure reduction determination system described in disclosure item (1), wherein the first acquisition processing unit acquires the rotational speed each time a predetermined acquisition timing arrives, the second acquisition processing unit acquires the resonant frequency based on the rotational speed acquired in accordance with the arrival of the acquisition timing each time the acquisition timing arrives, and the determination processing unit determines whether the difference between the last acquired resonant frequency and the reference frequency exceeds the first determination value when the resonant frequency acquired by the second acquisition processing unit at each acquisition timing increases beyond a predetermined second determination value, or decreases beyond a predetermined third determination value.

[0161] This system can automatically determine whether or not the type of pneumatic tire has been changed.

[0162] Disclosure item (4) is a tire pressure reduction determination system according to any of disclosure items (1) to (3), comprising a third acquisition processing unit that acquires driving condition information relating to the driving condition of the vehicle when the first acquisition processing unit acquires the rotational speed, and the second acquisition processing unit acquires the resonance frequency based on the rotational speed that is determined to be appropriate from the rotational speed acquired by the first acquisition processing unit based on the driving condition information acquired by the third acquisition processing unit.

[0163] This system makes it possible to avoid the acquisition of the resonant frequency based on the rotational speed acquired under driving conditions unsuitable for acquiring the resonant frequency.

[0164] Disclosure item (5) is a tire pressure reduction determination system according to any of disclosure items (1) to (4), wherein the pressure reduction determination process determines that the pneumatic tire is experiencing pressure reduction when the difference between the resonant frequency and the reference frequency based on the rotational speed acquired by the first acquisition processing unit exceeds a preset threshold, the preset value includes the threshold, and the modification processing unit changes the threshold to a value based on the maximum pressure reduction sensitivity among a plurality of pressure reduction sensitivities corresponding to a plurality of tire types when the determination processing unit determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value.

[0165] According to this system, a new threshold is set based on the highest of the multiple pressure reduction sensitivities corresponding to the multiple tire types. Therefore, compared to a configuration in which a new threshold is set based on a smaller pressure reduction sensitivity, it is possible to suppress the misjudgment that the air-filled tire is experiencing pressure loss even though the air pressure is within the normal range.

[0166] Disclosure item (6) is a tire pressure reduction determination method in which one or more processors perform the following steps: a first acquisition step of acquiring the rotational speed of a pneumatic tire mounted on a vehicle; a second acquisition step of acquiring the resonant frequency of the pneumatic tire based on the rotational speed acquired in the first acquisition step; a determination step of determining whether the difference between the resonant frequency acquired in the second acquisition step and a preset reference frequency exceeds a preset first determination value; and a modification step of changing a setting value used in a pressure reduction determination process that determines whether the pneumatic tire is depressurized based on the rotational speed acquired in the first acquisition step, if the determination step determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value.

[0167] This method, similar to the tire pressure reduction determination system in disclosure (1), makes it possible to suppress the decrease in accuracy of pressure reduction determination of the pneumatic tire caused by a change in the type of pneumatic tire.

[0168] Disclosure item (7) is a program for causing one or more processors to execute: a first acquisition step of acquiring the rotational speed of a pneumatic tire mounted on a vehicle; a second acquisition step of acquiring the resonant frequency of the pneumatic tire based on the rotational speed acquired in the first acquisition step; a determination step of determining whether the difference between the resonant frequency acquired in the second acquisition step and a preset reference frequency exceeds a preset first determination value; and a modification step of changing a setting value used in a depressurization determination process that determines whether the pneumatic tire is depressurizing based on the rotational speed acquired in the first acquisition step, if the determination step determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value.

[0169] According to this program, similar to the tire pressure reduction determination system in disclosure item (1), it is possible to suppress the decrease in accuracy of pressure reduction determination of the pneumatic tire caused by a change in the type of pneumatic tire.

[0170] Furthermore, this disclosure may also be a computer-readable recording medium on which the program described in disclosure item (7) is recorded non-temporarily. [Explanation of symbols]

[0171] Vehicle 1A 2 servers 3. Communication Network 10 tires 11 Control Unit 12 Operation display section 13 Communications Department 14 Storage section 15 GPS receivers 16 Wheel speed sensors 31 Control Unit 32 Operation display section 33 Communications Department 34 Storage section 51A First Acquisition Processing Unit 52 Third Acquisition Processing Unit 53 Appropriateness Determination Processing Unit 54A Second Acquisition Processing Unit 55 Pressure Depressure Determination Processing Unit 56 Notification Processing Unit 57 Update Processing Unit 58A Replacement Determination Processing Unit 59 Change Processing Unit 61 1st storage area 62 2nd storage area 63 Threshold storage unit 100A Tire Pressure Depressure Detection System

Claims

1. A first acquisition processing unit that acquires the rotational speed of a pneumatic tire mounted on a vehicle, A second acquisition processing unit acquires the resonant frequency of the pneumatic tire based on the rotational speed acquired by the first acquisition processing unit, A determination processing unit that determines whether the difference between the resonant frequency acquired by the second acquisition processing unit and a preset reference frequency exceeds a preset first determination value, When the determination processing unit determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value, a change processing unit changes the setting value used in the pressure reduction determination process, which determines whether or not the pneumatic tire is depressurized based on the rotational speed acquired by the first acquisition processing unit. A tire pressure reduction detection system equipped with the following features.

2. The first acquisition processing unit acquires the rotation speed when at least a predetermined specific operation is received. The second acquisition processing unit, upon receiving the specific operation, acquires the resonant frequency based on the rotational speed acquired in response to the acceptance of the specific operation. The aforementioned tire pressure reduction determination system is The system includes an update processing unit that updates the reference frequency based on the resonant frequency acquired in response to the acceptance of the specified operation, When the specified operation is received, the determination processing unit determines whether the difference between the reference frequency after updating by the update processing unit and the reference frequency before updating exceeds the first determination value. The tire pressure reduction determination system according to claim 1.

3. The first acquisition processing unit acquires the rotation speed each time a predetermined acquisition timing arrives. The second acquisition processing unit acquires the resonant frequency based on the rotational speed acquired in accordance with the arrival of the acquisition timing each time the acquisition timing arrives. The determination processing unit determines whether the difference between the last acquired resonant frequency and the reference frequency exceeds the first determination value when the resonant frequency acquired by the second acquisition processing unit at each acquisition timing increases beyond a preset second determination value, or decreases beyond a preset third determination value. The tire pressure reduction determination system according to claim 1.

4. The system includes a third acquisition processing unit that acquires driving condition information relating to the driving condition of the vehicle at the time the rotational speed is acquired by the first acquisition processing unit, The second acquisition processing unit acquires the resonant frequency based on the rotation speed that is determined to be appropriate from among the rotation speeds acquired by the first acquisition processing unit, based on the driving condition information acquired by the third acquisition processing unit. A tire pressure reduction determination system according to any one of claims 1 to 3.

5. In the pressure reduction determination process, if the difference between the resonant frequency and the reference frequency based on the rotational speed acquired by the first acquisition processing unit exceeds a preset threshold, it is determined that the pneumatic tire is experiencing pressure reduction. The aforementioned setting value includes the aforementioned threshold, The modification processing unit, when the determination processing unit determines that the difference between the resonance frequency and the reference frequency exceeds the first determination value, changes the threshold value to a value based on the maximum pressure reduction sensitivity among a plurality of pressure reduction sensitivities corresponding to a plurality of tire types. A tire pressure reduction determination system according to any one of claims 1 to 3.

6. A first acquisition step involves obtaining the rotational speed of the pneumatic tires mounted on the vehicle, A second acquisition step involves acquiring the resonant frequency of the pneumatic tire based on the rotational speed acquired in the first acquisition step, A determination step to determine whether the difference between the resonant frequency obtained by the second acquisition step and a preset reference frequency exceeds a preset first determination value, If the determination step determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value, a change step is made to change the setting value used in the pressure reduction determination process that determines whether or not the pneumatic tire is depressurized based on the rotational speed obtained in the first acquisition step. A tire pressure reduction determination method performed by one or more processors.

7. A first acquisition step involves obtaining the rotational speed of the pneumatic tires mounted on the vehicle, A second acquisition step involves acquiring the resonant frequency of the pneumatic tire based on the rotational speed acquired in the first acquisition step, A determination step to determine whether the difference between the resonant frequency obtained by the second acquisition step and a preset reference frequency exceeds a preset first determination value, If the determination step determines that the difference between the resonant frequency and the reference frequency exceeds the first determination value, a change step is made to change the setting value used in the pressure reduction determination process that determines whether or not the pneumatic tire is depressurized based on the rotational speed obtained in the first acquisition step. A program designed to run on one or more processors.

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