tire pressure monitoring system

Abstract

To provide a tire air pressure monitoring system that can appropriately determine abnormal decrease in tire air pressure due to an abnormality in a tire.SOLUTION: A tire air pressure monitoring system is applied to a vehicle 10 having a plurality of wheels 10a-10d including tires mounted on a vehicle body 11. The tire air pressure monitoring system comprises tire sensors 2 including air pressure detecting parts 21 that detect tire air pressure of the plurality of wheels 10a-10d, and an on-vehicle machine 3 including an abnormal decrease sensing part 331 that senses an abnormal decrease in tire air pressure due to an abnormality in the tire. The on-vehicle machine 3 calculates, as air pressure variations, variations of detected values from the air pressure detecting parts 21 in a predetermined period of time, and determines whether the tire air pressure decreases abnormally or not on the basis of a result of comparison of the air pressure variations with predetermined reference variations.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to tire pressure monitoring systems. [Background technology]

[0002] Some systems of this type warn the user when tire pressure falls below a legal threshold, but they cannot determine whether the drop in tire pressure is due to a natural air leak caused by changes in outside temperature or a tire abnormality. If there is an abnormality in the tire, the tire pressure will drop again even if the tire is inflated normally.

[0003] In contrast, the system described in Patent Document 1 below determines an abnormal drop in tire pressure due to a tire abnormality by comparing the difference between the absolute value of the tire pressure of each tire and a fixed reference value, and the difference between the absolute values of the air pressure between each tire and a fixed reference value. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-76748 Summary of the Invention [Problem to be solved by the invention]

[0005] However, tire pressures are not always adjusted to the same pressure on the same day. Therefore, when determining whether or not tire pressures have dropped abnormally based on the difference between the absolute tire pressure of each tire and a fixed reference value, or the difference between the absolute tire pressures of each tire and a fixed reference value, as in Patent Document 1, the difference in tire pressures between each tire due to differences in tire pressure adjustment dates may be erroneously determined as an abnormal drop in tire pressure. Furthermore, the reference tire pressure value varies depending on the type of tire, the vehicle on which it is installed, etc.

[0006] An object of the present disclosure is to provide a tire pressure monitoring system that can appropriately determine an abnormal drop in tire pressure caused by an abnormality in the tire. [Means for solving the problem]

[0007] Claim 1 and claim 5 The invention described in A tire pressure monitoring system applied to a vehicle (10) having a body (11) and a plurality of wheels (10a, 10b, 10c, 10d) including tires attached thereto, a tire sensor (2) including an air pressure detection unit (21) for detecting tire air pressures of a plurality of wheels; an abnormal drop detection unit (331) that detects an abnormal drop in tire air pressure caused by an abnormality in the tire; The abnormal drop detection unit calculates the amount of change in the value detected by the air pressure detection unit over a predetermined period as the amount of change in air pressure, and determines whether or not there is an abnormal drop based on a comparison between the amount of change in air pressure and a predetermined reference amount of change. In the invention as recited in claim 1, the abnormal drop detection unit sets the reference change amount based on the smallest change amount of air pressure among the air pressure changes in the plurality of wheels. In the invention described in claim 5, the abnormal drop detection unit counts the number of times the amount of change in air pressure exceeds a reference amount of change as a leak counter, and determines that an abnormal drop has occurred when the leak counter reaches a determination threshold value.

[0008] Unlike the difference between the absolute tire pressure of each tire and a fixed reference value, or the comparison of the difference between the absolute tire pressures of each tire and a fixed reference value, the change in the detected value over a predetermined period is hardly affected by the difference in the tire pressure adjustment date. Therefore, by comparing the change in the detected value over a predetermined period with the reference change to determine whether or not there is an abnormal drop in tire pressure, it is possible to more appropriately determine whether or not there is an abnormal drop in tire pressure due to a tire abnormality than with conventional technology. This enables early detection of potential tire abnormalities, thereby improving vehicle safety and usability.

[0009] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and the specific components described in the embodiments described below. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is an overall configuration diagram of a tire pressure monitoring system according to a first embodiment. [Figure 2] FIG. 2 is a block diagram of a tire sensor. [Figure 3] FIG. 2 is a block diagram of an in-vehicle device. [Figure 4] FIG. 3 is an explanatory diagram for explaining changes in tire air pressure over time. [Figure 5] FIG. 10 is an explanatory diagram for explaining a change in tire air pressure when a slow puncture occurs. [Figure 6] FIG. 10 is an explanatory diagram for explaining a change in tire air pressure when a slow puncture occurs in the left front wheel. [Figure 7] 10 is a flowchart showing a flow of an abnormal decrease detection process executed by the vehicle-mounted device. [Figure 8] 4 is an explanatory diagram for explaining a method for detecting an abnormal decrease in tire air pressure in the abnormal decrease detection process according to the first embodiment. FIG. [Figure 9] 10A and 10B are explanatory diagrams for explaining a modified example of a method for detecting an abnormal drop in tire air pressure. [Figure 10] 10 is an explanatory diagram for explaining a method for detecting an abnormal decrease in tire air pressure in the abnormal decrease detection process according to the second embodiment. FIG. [Figure 11] 10A and 10B are explanatory diagrams for explaining a modified example of a method for detecting an abnormal drop in tire air pressure. [Figure 12] FIG. 10 is a block diagram of an in-vehicle device according to a third embodiment. [Figure 13] 10 is a flowchart showing the flow of an abnormal decrease detection process executed by an in-vehicle device according to a third embodiment. [Figure 14] FIG. 10 is a block diagram of a tire sensor according to a fourth embodiment. [Figure 15] FIG. 4 is an explanatory diagram for explaining correction of tire air pressure. [Figure 16] 10 is a flowchart showing a flow of an abnormal decline detection process executed by an in-vehicle device according to a fourth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same as or equivalent to those described in the preceding embodiments will be given the same reference numerals, and their description may be omitted. Furthermore, in the embodiments, when only some of the components are described, the components described in the preceding embodiments can be applied to the remaining components. The following embodiments can be partially combined with each other, even if not specifically stated, as long as there is no particular problem with the combination.

[0012] (First embodiment) This embodiment will be described with reference to Figs. 1 to 8. Fig. 1 is a diagram showing a tire pressure monitoring system (hereinafter referred to as TPMS) having a tire pressure detection function. The front, rear, left and right shown in Fig. 1 refer to the front, rear, left and right of a vehicle 10. In the following description, when the four wheels 10a to 10d attached to the vehicle 10 are to be distinguished from one another, the four wheels 10a to 10d may be referred to as a left front wheel FL, a right front wheel FR, a left rear wheel RL and a right rear wheel RR.

[0013] As shown in Fig. 1, the TPMS includes a plurality of tire sensors 2 and an on-board device 3. The TPMS monitors tire pressure using each tire sensor 2 and on-board device 3, and notifies the user of the monitoring results via a notification unit such as a meter 5. The TPMS also calculates the amount of change in tire pressure detected by an air pressure detection unit 21 over a predetermined period as an air pressure change amount ΔP t The air pressure change ΔP t and a predetermined reference change amount ΔP th The presence or absence of an abnormal decrease is determined based on a comparison with the tire pressure detection unit 21. For ease of explanation, the tire pressure detection value of the tire pressure detection unit 21 may be simply referred to as the "detection value of the tire pressure detection unit 21" below.

[0014] The tire sensors 2 are attached to the wheels 10a-10d, detect the air pressure of the tires attached to the wheels 10a-10d, and transmit the tire pressure information indicating the detection results stored in a frame. The vehicle-mounted device 3 is attached to the vehicle body 11 of the vehicle 10, and receives the frames transmitted from the tire sensors 2 and performs various processes and calculations based on the information stored therein to detect tire air pressure.

[0015] As shown in FIG. 2, the tire sensor 2 includes an air pressure detection unit 21, an acceleration sensor 22, a first microcomputer 23, and a tire radio 24, and each unit is driven by power supplied from a battery (not shown).

[0016] The air pressure detection unit 21 includes a pressure sensor 21a and a temperature sensor 21b, and outputs a detection signal corresponding to the tire air pressure and the temperature inside the tire. The acceleration sensor 22 is used to detect the rotation angle of the tire sensor 2 and the traveling speed (i.e., vehicle speed) of the vehicle 10. The acceleration sensor 22 is configured, for example, as a two-axis acceleration sensor capable of detecting the radial acceleration and circumferential acceleration of each of the wheels 10a to 10d.

[0017] The first microcomputer 23 constitutes the control unit of the tire sensor 2 and includes a CPU, memories such as ROM and RAM, and I / O. The first microcomputer 23 executes predetermined processes according to programs stored in the built-in memory. The memory stores individual ID information including a unique tire ID for identifying each tire sensor 2 and a vehicle ID unique to the vehicle for identifying the host vehicle.

[0018] The first microcomputer 23 receives, for example, detection signals from the pressure sensor 21a and the temperature sensor 21b, processes them and, if necessary, processes them, and stores the information relating to the tire pressures together with the ID information of each tire sensor 2 in a frame.

[0019] The first microcomputer 23 also monitors the detection signal from the acceleration sensor 22 and performs vehicle movement determination to determine the angle of each tire sensor 2 and whether the vehicle 10 is moving. After creating a frame, the first microcomputer 23 transmits the frame from the tire radio 24 to the in-vehicle device 3 based on the result of the vehicle movement determination. Hereinafter, information related to tire pressure will also be simply referred to as tire information. Specifically, the first microcomputer 23 repeatedly transmits frames at predetermined timings while the vehicle 10 is moving.

[0020] The tire radio 24 includes a first transmission / reception circuit 241 and a first communication antenna 242. The first transmission / reception circuit 241 is a communication circuit that performs bidirectional communication with the in-vehicle device 3 via the first communication antenna 242. The first transmission / reception circuit 241 performs wireless communication based on a communication method such as BLE. BLE is an abbreviation for Bluetooth (registered trademark) Low Energy. Note that the first transmission / reception circuit 241 may perform wireless communication based on a communication method other than BLE.

[0021] The first communication antenna 242 is an antenna for two-way communication with the vehicle-mounted device 3. By including the tire radio 24, the tire sensor 2 is able to perform two-way communication with the vehicle-mounted device 3, not just one-way communication from the tire sensor 2 to the vehicle-mounted device 3.

[0022] The tire sensor 2 configured in this manner detects the tire air pressure and the temperature inside the tire, and while the vehicle 10 is running, transmits a frame at a timing when the angle of the tire sensor 2 reaches a predetermined angle.

[0023] On the other hand, the on-vehicle device 3 is provided in the vehicle body 11. As shown in Fig. 3, the on-vehicle device 3 includes an on-vehicle radio device 31 and a second microcomputer 33. The on-vehicle device 3 is connected to a meter 5, a mobile communication device 6, and the like via an in-vehicle LAN (Local Area Network) such as a CAN (Controller Area Network).

[0024] The in-vehicle radio 31 includes a second communication antenna 311 and a second transmission / reception circuit 312. The second communication antenna 311 is an antenna for performing bidirectional communication with each tire sensor 2. The second communication antenna 311 is used not only to receive frames and the like sent from each tire sensor 2, but also to transmit signals to each tire sensor 2. The second communication antenna 311 may be an internal antenna disposed within the main body of the in-vehicle radio 3, or may be an external antenna with wiring extending from the main body.

[0025] The second transmission / reception circuit 312 is a communication circuit that communicates bidirectionally with each tire sensor 2 via the second communication antenna 311. The second transmission / reception circuit 312 performs wireless communication based on a communication method such as BLE. The second transmission / reception circuit 312 functions as an input unit that inputs transmission frames received from each tire sensor 2 via the second communication antenna 311 and sends the frames to the second microcomputer 33. When the second transmission / reception circuit 312 receives a frame via the second communication antenna 311, it transmits the received signal to the second microcomputer 33.

[0026] The second microcomputer 33 constitutes a control unit in the vehicle-mounted device 3 and includes a CPU, memories such as ROM and RAM, an I / O, etc. The second microcomputer 33 executes a tire pressure detection process and an abnormal drop detection process for detecting an abnormal drop in tire pressure caused by a tire abnormality, according to a program stored in the built-in memory. In this embodiment, the configuration for executing the abnormal drop detection process in the vehicle-mounted device 3 constitutes the abnormal drop detection unit 331.

[0027] The meter 5 is a display unit provided in the vehicle cabin that displays various information. The meter 5 displays various information when the power is on, specifically when an accessory switch (hereinafter referred to as ACC) or a start switch such as an ignition switch IG is turned on. The display on the meter 5 is basically performed when the power is on.

[0028] The meter 5 is arranged in a location visible to the driver, and is configured, for example, by a multi-information display installed in the instrument panel of the vehicle 10, a display of a navigation device, or the like. For example, when a signal indicating a drop in tire air pressure is sent from the in-vehicle device 3, the meter 5 notifies the driver of the drop in tire air pressure of the wheel 10a-10d by identifying the wheel 10a-10d and displaying a display indicating the drop in tire air pressure. In this embodiment, the meter 5 configures the "notification unit."

[0029] The mobile communication device 6 is a wireless communication unit for communicating with communication destinations outside the vehicle 10. When the ignition switch IG is turned on, the mobile communication device 6 becomes active and wirelessly connects to a wireless base station 61 connected to a communication network 62, thereby communicating with a service center 63 and a cloud server 64 connected to the communication network 62.

[0030] The service center 63 acquires various types of information via the communication network 62 and communicates with a user terminal (not shown) (a terminal carried by the user of the vehicle 10) via the communication network 62. The cloud server 64 is a server created in a cloud environment and stores various types of information. The in-vehicle device 3 is able to acquire various types of information stored in the cloud server 64 via the communication network 62.

[0031] The TPMS configured as above monitors the tire pressure of each of the wheels 10a to 10d through a tire pressure detection process and a tire pressure abnormal drop detection process. The tire pressure detection process and the tire pressure abnormal drop detection process are executed periodically or irregularly by the TPMS on-board device 3.

[0032] The tire pressure detection process detects the tire pressures of the wheels 10a-10d to which the tire sensors 2 are attached. Specifically, the vehicle-mounted device 3 detects the tire pressures of the wheels 10a-10d by calculating a tire pressure equivalent value at a predetermined temperature based on the ID information and tire information stored in the transmission frame from each tire sensor 2. An electrical signal corresponding to the tire pressure detection result is then output to the meter 5 via an in-vehicle LAN such as a CAN. For example, the vehicle-mounted device 3 outputs a signal indicating the tire pressure of each wheel 10a-10d to the meter 5. The vehicle-mounted device 3 detects a decrease in tire pressure by comparing the tire pressure detection result with a predetermined alarm threshold, and upon detecting a decrease in tire pressure, outputs a signal to that effect to the meter 5. This notifies the meter 5 of a decrease in the tire pressure of one or more of the four wheels 10a-10d, and the decrease is displayed on the meter 5. In this way, the tire pressure detection process issues an alarm when the tire pressure drops to the abnormal pressure value Pth, as shown in FIG. 4.

[0033] However, if a warning is issued after the tire pressure has dropped to the abnormal pressure value Pth, there is a high possibility that the driver will continue driving unless a warning is issued, which will lead to a decrease in fuel economy and deterioration of the tire condition.

[0034] Furthermore, since the temperature of the tires rises when the vehicle 10 is driven, the tire temperature tends to be higher immediately after the driver gets off the vehicle than immediately before the driver gets on. Tire pressure increases when the tire temperature is high and decreases when the tire temperature is low. For this reason, tire pressure tends to be lower immediately after the driver gets on the vehicle than immediately before the driver gets off the vehicle. Furthermore, since the tire pressure often drops to an abnormal pressure value Pth between the time the driver gets off the vehicle and the time he gets on the next day, causing an alarm to be issued, it is desirable to notify the driver before an abnormality occurs.

[0035] Factors that cause a drop in tire air pressure include slow punctures. Examples of causes of slow punctures include gaps that occur between the wheel rim and the bead of the tire, the end of life or damage to the valve core of the air valve, small holes or cracks in the tire, accidental punctures during inflation, and gaps that occur when sand gets caught in the tire while driving on rough roads. Slow punctures generally do not occur simultaneously on all wheels 10a-10d. If slow punctures occur on only some of the wheels 10a-10d, significant differences in the amount of change in tire air pressure for each wheel 10a-10d over a given period occur. For example, as shown in FIG. 5, the tire air pressure of each wheel 10a-10d that has experienced a slow puncture changes more significantly over a given period than tire air pressures that show a normal downward trend.

[0036] Here, the tire pressure adjustment date t0 to the present time t a The amount of change in tire pressure is the amount of change in tire pressure ΔP t can be calculated using the following formula F1. a The rate of change in tire pressure is the air decrease rate δ shown in the following formula F2 t It can be calculated as:

[0037] ΔP t =P0-P t ···(F1) δ t =ΔP t / (t a -t0) ···(F2) When a slow puncture occurs, the air pressure change amount ΔP of each wheel 10a to 10d increases. t and air reduction rate δ t For example, as shown in Figure 6, when a slow puncture occurs in the left front tire FL, the air reduction rate δ t The change in tire pressure of the right rear wheel RR is the smallest ΔP aRR Compared to the change in tire pressure of the left front wheel FL, ΔP aFL becomes larger.

[0038] In consideration of these circumstances, the TPMS of the present disclosure executes an abnormal drop detection process for detecting an abnormal drop in tire air pressure in the onboard device 3. The abnormal drop detection process will be described below with reference to Fig. 7. The abnormal drop detection process shown in Fig. 7 is started, for example, when the tire air pressure is adjusted.

[0039] 7, in step S100, the on-vehicle device 3 acquires the tire pressure of each tire on the day the tire pressure was adjusted from the tire sensor 2 and stores the acquired tire pressure in memory as an initial value P0. The on-vehicle device 3 also acquires the time when the tire pressure was adjusted as the pressure adjustment date t0 via another ECU. Note that in the processing of step S100, the tire pressures of all tires mounted on the vehicle 10 are acquired, not just the tire whose pressure was adjusted.

[0040] Next, in step S110, the vehicle-mounted device 3 receives the tire pressures "P t Then, in step S120, the vehicle-mounted device 3 acquires the tire air pressures "P t The warning threshold is set to, for example, the minimum tire pressure specified by regulations.

[0041] The tire pressure of each wheel 10a to 10d is "P t If " is less than the predetermined warning threshold, the vehicle-mounted device 3 outputs a low-pressure warning to notify the user of a drop in tire air pressure via the meter 5 in step S130, and then exits this process.

[0042] On the other hand, the tire air pressure of each wheel 10a to 10d “P t If the tire pressure "P" is equal to or greater than the predetermined warning threshold value, the vehicle-mounted device 3 changes the tire pressure "P" from the initial tire pressure value P0 to the current tire pressure "P" in step S140. t " to calculate the air pressure change ΔP t That is, the vehicle-mounted device 3 sets the value detected by the air pressure detection unit 21 when the tire air pressure was previously adjusted as an initial value P0, and calculates the air pressure change amount ΔP by subtracting the current value detected by the air pressure detection unit 21 from the initial value P0.t It is calculated as follows.

[0043] Next, in step S150, the vehicle-mounted device 3 sets a reference value that serves as a determination threshold for determining a drop in tire air pressure. As described above, slow punctures do not generally occur simultaneously for each of the wheels 10a to 10d. Then, for at least each of the wheels 10a to 10d, the amount of change in air pressure ΔP t In view of this, the vehicle-mounted device 3 calculates the air pressure change amount ΔP of each of the wheels 10a to 10d. t The reference change amount ΔP is calculated based on the smallest one of the above. th Set to.

[0044] The vehicle-mounted device 3 calculates the air pressure change amount ΔP of each of the wheels 10a to 10d. t The smallest of these is the reference value ΔP t_min and the reference value ΔP t_min is multiplied by a predetermined coefficient α (for example, 1.5) to obtain the reference change amount ΔP th For example, in the example shown in FIG. 6, the change in tire air pressure of the right rear wheel RR is set to ΔP aRR is smallest, so the change in tire pressure of the right rear wheel RR is ΔP aRR Based on the reference change amount ΔP th will be set.

[0045] Next, in step S160, the vehicle-mounted device 3 calculates the air pressure change amount ΔP t and a predetermined reference change amount ΔP th In this determination process, for example, the tire pressure change amount ΔP t is the reference change amount ΔP th Then, it is determined whether the air pressure change amount ΔP t is the reference change amount ΔP th In the above cases, it is determined that there is an instantaneous pressure drop, and the amount of air pressure change ΔP t is ΔP th If the value is less than this, it is determined that there is no instantaneous pressure drop.

[0046] If the result of the determination process in step S160 is that there is an instantaneous pressure drop, the vehicle-mounted device 3 increments the leak counter CNT in step S170. The leak counter CNT counts up the air pressure change amount ΔP t is the reference change amount ΔP th The number of times it has exceeded this.

[0047] Here, the air pressure change amount ΔP t and the reference change ΔP th The greater the difference between the tire pressure change amount ΔP and the tire pressure change amount ΔP, the greater the possibility that an abnormal decrease in tire pressure has occurred. t and the reference change ΔP th The larger the difference between the air pressure change amount ΔP and the in-vehicle device 3, the larger the count value X to be added to the leak counter CNT. t and the reference change ΔP th The difference between this and the reference value ΔP t_min The count value X is set to "1" for 1.5 to 2 times the reference value ΔP t_min The count value X is set to "2" for 2 to 2.5 times the reference value ΔP t_min If the count value X exceeds 2.5 times the value of the leak current, the count value X to be added to the leak counter CNT is set to "4".

[0048] When the leak counter CNT reaches a certain value, it is considered that the drop in tire air pressure is not instantaneous but constant, i.e., when the leak counter CNT reaches a certain value, it is considered that an abnormal drop in tire air pressure has occurred.

[0049] Therefore, in step S180, the vehicle-mounted device 3 determines whether the leak counter CNT satisfies the warning condition. Specifically, the vehicle-mounted device 3 determines whether the leak counter CNT has exceeded a predetermined judgment threshold, and determines that the leak counter CNT satisfies the warning condition when the leak counter CNT has exceeded the predetermined judgment threshold.

[0050] If the leak counter CNT does not satisfy the alarm condition, the vehicle-mounted device 3 returns to step 110 and receives the tire air pressures "P" of the respective wheels 10a to 10d from the tire sensors 2. t The process of step S110 is executed after a predetermined time has elapsed since the previous execution of the process of step S110.

[0051] If the leak counter CNT satisfies the alarm condition, the in-vehicle device 3 proceeds to step 190, outputs an alarm via the meter 5 to the effect that an abnormal drop in tire air pressure has occurred due to a slow puncture or the like, and then exits this processing. In this alarm, it is desirable to issue a message urging the user to check the tire in a form that is easy for the user to recognize.

[0052] On the other hand, if the result of the determination process in step S160 is that there is no momentary abnormal drop, the vehicle-mounted device 3 resets the leak counter CNT to zero in step S200, and then returns to step S110.

[0053] In the TPMS described above, the amount of change in the value detected by the tire pressure detection unit 21 over a predetermined period is calculated as the tire pressure change amount ΔP t The air pressure change amount ΔP t and a predetermined reference change amount ΔP th The presence or absence of an abnormal drop in tire air pressure is determined based on a comparison with the reference value. The amount of change in the detected value of the air pressure detection unit 21 over a predetermined period is hardly affected by the difference in the tire air pressure adjustment date, unlike the comparison between the difference between the absolute value of the tire air pressure of each tire and a fixed reference value and the comparison between the difference in the absolute value of the air pressure between each tire and a fixed reference value. For this reason, the amount of change in the detected value of the air pressure detection unit 21 over a predetermined period is used as the reference change amount ΔP th By comparing the tire pressure with the tire pressure sensor to determine whether or not there is an abnormal drop in tire pressure, it is possible to more appropriately determine whether or not there is an abnormal drop in tire pressure due to a tire abnormality than with conventional technology. This makes it possible to detect potential tire abnormalities early, thereby improving the safety and usability of the vehicle 10.

[0054] (1) The above-mentioned predetermined period is the period from the last tire pressure adjustment of at least one of the plurality of tires to the present. The vehicle-mounted device 3 sets the detection value of the tire pressure detection unit 21 at the time of the last tire pressure adjustment as an initial value P0, and calculates the pressure change amount ΔP by subtracting the current detection value of the tire pressure detection unit 21 from this initial value P0. t It is calculated as follows.

[0055] In a situation where tire pressure gradually decreases due to slow puncture, the amount of change in tire pressure in a short period (for example, one day) (i.e., the amount of change in tire pressure P t This can make it difficult to determine if the tire pressure is abnormally low.

[0056] In contrast, the amount of change in tire pressure from when the tire pressure was adjusted to the normal pressure until now is greater than the amount of change in tire pressure over a short period of time (for example, one day).This makes it possible to appropriately determine an abnormal decrease in tire pressure even when the tire pressure gradually decreases due to slow puncture.

[0057] (2) The vehicle-mounted device 3 detects the air pressure change amount ΔP of the plurality of wheels 10a to 10d. t The reference change amount ΔP is calculated based on the smallest one of the above. th It is rare that an abnormality occurs simultaneously in the tires of the wheels 10a to 10d attached to the same vehicle 10. For this reason, the amount of change in air pressure ΔP t The reference change amount ΔP is calculated based on the smallest one of the above. th By setting the above, it is possible to appropriately determine whether an abnormal decrease in tire air pressure is caused by an abnormality in the tire.

[0058] Here, when determining whether or not there is an abnormal drop in tire pressure from the difference between the absolute value of the tire pressure of each tire and a fixed reference value, as in the prior art, it is necessary to set the reference value according to the type of tire on the wheels 10a to 10d, the reference internal pressure, the usage environment, etc. For example, every time the tires are replaced with different types of tires, it is necessary to reset the reference value, which is a cumbersome task.

[0059] In contrast, the tire air pressure change amount ΔP of the wheels 10a to 10d attached to the same vehicle 10 t The reference change amount ΔP is calculated based on the smallest one of the above. th By setting the above, it is not necessary to match the tire type, reference internal pressure, usage environment, etc. of the wheels 10a to 10d. This makes it possible to reduce the complicated work of determining whether the tire pressure has dropped abnormally.

[0060] (3) The on-board device 3 detects the air pressure change amount ΔP t is the reference change amount ΔP th The number of times that the leak counter CNT exceeds this threshold is counted as a leak counter CNT, and when the leak counter CNT reaches a determination threshold, it is determined that an abnormal drop has occurred. In this way, if a tire pressure abnormal drop is determined when a drop in tire pressure is detected multiple times, it is possible to prevent momentary fluctuations in tire pressure due to the running state of the vehicle 10 or the like from being erroneously determined as an abnormal drop in tire pressure.

[0061] (4) The on-board device 3 detects the amount of change in air pressure ΔP t and the reference change ΔP th The greater the difference between the air pressure change amount ΔP and the air pressure change amount ΔP, the larger the count value X to be added to the leak counter CNT. t and the reference change ΔP th The greater the difference between the two, the higher the possibility of an abnormal drop in tire pressure. t and the reference change ΔP th It is desirable to increase the count value X to be added to the leak counter CNT as the difference between

[0062] (5) The on-board device 3 detects the amount of change in air pressure ΔP tis the reference change amount ΔP th If the tire pressure is equal to or less than this value, the leak counter CNT is reset to zero. The leak counter CNT may be incremented due to a momentary change in tire pressure caused by the running state of the vehicle 10, etc. For this reason, the amount of change in tire pressure ΔP t is the reference change amount ΔP th It is desirable to reset the leak counter CNT to zero when:

[0063] (Modification of the first embodiment) In the first embodiment, the air pressure change amount ΔP t The reference change amount ΔP is calculated based on the smallest one of the above. th However, the reference change amount ΔP th The method for setting the reference change amount ΔP is not limited to this. th For example, the tire pressure may be set based on the amount of change in tire pressure over a predetermined period estimated from tire pressure data for the same or similar tire type and mounting conditions. The tire pressure data is, for example, data that defines the relationship between the amount of change in tire pressure and the time elapsed since the tire pressure was adjusted. This also makes it possible to appropriately determine an abnormal drop in tire pressure due to a tire abnormality. The amount of change in tire pressure over a predetermined period may be estimated, for example, by acquiring tire pressure data from the service center 63 or cloud server 64 via the communication network 62 and using the acquired tire pressure data and the time elapsed since the tire pressure was adjusted. The tire pressure data may, for example, be data that associates the time elapsed since the tire pressure was adjusted with the average amount of change in tire pressure.

[0064] The amount of change in tire pressure estimated from the air pressure data is set as the reference value ΔP t_std and the reference value ΔP t_std Based on the reference change amount ΔP th When setting, the air pressure change amount ΔP t and the reference change ΔP th It is desirable to increase the count value X as the difference between the air pressure change amount ΔP tand the reference change ΔP th The difference between this and the reference value ΔP t_std The count value X is set to "1" for 1.5 to 2 times the reference value ΔP t_std The count value X can be set to "2" for 2 to 2.5 times the reference value ΔP t_std If the count value X exceeds 2.5 times the value of the first embodiment, the count value X is set to "4." This modification is not limited to the first embodiment, but also applies to the following embodiments.

[0065] (Second embodiment) Next, a second embodiment will be described with reference to Fig. 10. In this embodiment, differences from the first embodiment will be mainly described.

[0066] The vehicle-mounted device 3 of the first embodiment calculates the tire air pressure change amount ΔP t and the reference change ΔP th The larger the difference between the air pressure change amount ΔP and the in-vehicle device 3 of this embodiment, the larger the count value X to be added to the leak counter CNT. t and the reference change ΔP th The larger the difference between the reference value ΔP and the vehicle-mounted device 3, the smaller the determination threshold value is set. t_min The judgment threshold is maintained at the initial "N" up to 1.5 times the reference value ΔP t_min When the value becomes 1.5 to 2 times larger than the reference value ΔP, the judgment threshold is changed to "(2 / 3)N". t_min When the reference value ΔP is 2.0 to 2.5 times, the judgment threshold is changed to "(1 / 3)N". t_std If it exceeds 2.5 times, the judgment threshold should be set to "(1 / 3)N" or less.

[0067] The rest of the configuration is the same as that of the first embodiment. The TPMS of this embodiment can obtain the same effects as those of the first embodiment that are achieved by a configuration common to or equivalent to that of the first embodiment.

[0068] (1) Air pressure change ΔP t and the reference change ΔP thThe greater the difference between the two, the higher the possibility of an abnormal drop in tire pressure. t and the reference change ΔP th It is desirable to make the determination threshold smaller as the difference between

[0069] (Modification of the second embodiment) In the second embodiment, the air pressure change amount ΔP t The reference change amount ΔP is calculated based on the smallest one of the above. th However, the reference change amount ΔP th The method for setting the reference change amount ΔP is not limited to this. th For example, the tire pressure change amount may be set based on the amount of change in tire pressure over a predetermined period estimated from tire pressure data that defines the relationship between the time elapsed since the tire pressure adjustment and the amount of change in tire pressure. This also makes it possible to appropriately determine whether the tire pressure has dropped abnormally due to a tire abnormality. Note that this modification is not limited to the second embodiment, and is similar to the following embodiments.

[0070] The amount of change in tire pressure estimated from the air pressure data is the reference value ΔP t_std and the reference value ΔP t_std Based on the reference change amount ΔP th When setting, the air pressure change amount ΔP t and the reference change ΔP th For example, as shown in FIG. 11, the difference between the air pressure change amount ΔP t and the reference change ΔP th The difference between this and the reference value ΔP t_std The judgment threshold is set to "N" up to 1.5 times the reference value ΔP t_std If the threshold value is 1.5 to 2 times larger than the reference value ΔP, the threshold value should be changed to "(2 / 3)N". t_std If the value is 2.0 to 2.5 times larger than the threshold value, the threshold value can be changed to "(1 / 3)N".

[0071] (Third embodiment) Next, a third embodiment will be described with reference to Figures 12 and 13. In this embodiment, differences from the first embodiment will be mainly described.

[0072] The tire pressure changes depending on the tire internal temperature Tt, which is the temperature inside the tire. If the tire internal temperature Tt of each tire is different, the tire pressure of each tire will be different due to the difference. In addition, the tire pressure is changed from the tire pressure adjustment date t0 to the current time t a If the internal tire temperature Tt is different between the two, the tire pressure will be different due to the difference. These changes in tire pressure due to the internal tire temperature Tt can be a factor that reduces the accuracy of determining an abnormal drop in tire pressure caused by a tire abnormality.

[0073] Taking these factors into consideration, the vehicle-mounted device 3 of this embodiment is equipped with a pressure correction unit 332 that corrects the tire air pressure detection value in the air pressure detection unit 21 to a reference pressure value, which is the pressure at a predetermined reference temperature, based on the tire internal temperature Tt, as shown in Figure 12.

[0074] The pressure corrector 332 converts the tire pressure detected by the pressure detector 21 into a reference pressure value at a predetermined reference temperature, for example, by referring to a map or a relational expression that defines the relationship between changes in tire internal temperature Tt and changes in tire pressure. For example, the pressure corrector 332 determines the temperature difference between the detection value of the temperature sensor 21b and the reference temperature, and calculates the reference pressure value based on the temperature difference, the tire pressure detected by the pressure detector 21, and the map or relational expression.

[0075] Here, the reference temperature is stored in the memory of the second microcomputer 33. The reference temperature is set, for example, to a standard temperature (e.g., 25°C), and is set to a common value for each tire. The reference temperature is not limited to a predetermined fixed value, and may be a variable value. The reference temperature may be set to the tire internal temperature Tt of any one of the tires on the pressure adjustment date t0 or the average value of the tire internal temperatures Tt of each tire.

[0076] In the abnormal drop detection process, the vehicle-mounted device 3 calculates the amount of change in air ΔP using the reference pressure value corrected by the pressure correction unit 332. t The abnormal decrease detection process of this embodiment will be described below with reference to Fig. 13. The abnormal decrease detection process shown in Fig. 13 is started, for example, when the tire pressure is adjusted.

[0077] 13, in step S100A, the vehicle-mounted device 3 calculates a reference pressure value for each tire based on the tire pressure and internal tire temperature Tt of each tire on the day the tire pressure was adjusted. That is, the vehicle-mounted device 3 corrects the tire pressure detected by the tire pressure detection unit 21 of each tire on the day the tire pressure was adjusted to a reference pressure value, which is the pressure at a predetermined reference temperature, based on the internal tire temperature Tt of each tire. Note that in the processing of step S100A, the reference pressure values are calculated for all tires mounted on the vehicle 10, not just the tire whose pressure has been adjusted.

[0078] Next, in step S105A, the on-board device 3 stores the reference pressure value in memory as an initial value P0. The on-board device 3 also acquires, via another ECU, the time when the tire pressure was adjusted as the pressure adjustment date t0.

[0079] Next, in step S110A, the vehicle-mounted device 3 calculates a reference pressure value for each tire based on the tire pressure and internal tire temperature Tt of each tire. That is, the vehicle-mounted device 3 corrects the tire pressure detected by the pressure detection unit 21 of each tire to a reference pressure value that is the pressure at a predetermined reference temperature based on the internal tire temperature Tt of each tire. The predetermined reference temperature here is the same temperature as the reference temperature on the day the tire pressure was adjusted.

[0080] Next, in step S115A, the vehicle-mounted device 10 converts the reference pressure value obtained in step S110A into the tire pressure "P t Then, in step S120A, the vehicle-mounted device 3 sets the tire air pressures of the wheels 10a to 10d to "P tThe warning threshold is set to, for example, the minimum tire pressure specified by regulations.

[0081] The tire pressure of each wheel 10a to 10d is "P t If " is less than the predetermined warning threshold, the vehicle-mounted device 3 outputs a low-pressure warning to notify the user of a drop in tire pressure via the meter 5 in step S130A, and then exits this process.

[0082] On the other hand, the tire air pressure of each wheel 10a to 10d “P t If the tire pressure "P" is equal to or greater than the predetermined warning threshold value, the vehicle-mounted device 3 changes the tire pressure "P" from the initial tire pressure value P0 to the current tire pressure "P" in step S140A. t " to calculate the air pressure change ΔP t That is, the abnormal drop detection unit 331 of the in-vehicle device 3 sets the reference pressure value calculated by the pressure correction unit 332 when the tire pressure was previously adjusted as an initial value P0, and calculates the air pressure change amount ΔP by subtracting the current reference pressure value calculated by the pressure correction unit 332 from the initial value P0. t It is calculated as follows.

[0083] The subsequent processes of steps S150A, S160A, S170A, S180A, S190A, and S200A are the same as the processes of steps S150, S160, S170, S180, S190, and S200 described in the first embodiment, and therefore will not be described again.

[0084] The rest of the configuration is the same as that of the first embodiment. The TPMS of this embodiment can obtain the same effects as those of the first embodiment that are achieved by a configuration common to or equivalent to that of the first embodiment.

[0085] Furthermore, the TPMS of this embodiment has the following advantages. (1) The TPMS of this embodiment includes a pressure correction unit 332 that corrects the tire pressure detected by the tire pressure detection unit 21 to a reference pressure value, which is the pressure at a predetermined reference temperature, based on the tire internal temperature Tt, which is the temperature inside each tire. The abnormal drop detection unit 331 of the vehicle-mounted device 3 sets the reference pressure value calculated by the pressure correction unit 332 when the tire pressure was last adjusted as an initial value P0, and calculates the air pressure change amount ΔP by subtracting the current reference pressure value calculated by the pressure correction unit 332 from the initial value P0. t It is calculated as follows.

[0086] In this way, the tire pressure change amount ΔP is calculated by subtracting the current reference pressure value from the reference pressure value corrected at the previous tire pressure adjustment. t Then, the amount of change in air pressure ΔP t is hardly affected by the difference in tire internal temperature Tt from the tire pressure adjustment date. t By comparing the measured value with a reference change amount to determine whether or not there is an abnormal drop in tire air pressure, it is possible to more appropriately determine whether or not there is an abnormal drop in tire air pressure due to a tire abnormality than with conventional techniques.

[0087] (Modification of the third embodiment) The in-vehicle device 3 of the TPMS of the third embodiment, like the second embodiment, t and the reference change ΔP th The larger the difference between the two, the smaller the determination threshold value may be. This also applies to the following embodiments.

[0088] (Fourth embodiment) Next, a fourth embodiment will be described with reference to Figures 14 to 16. In this embodiment, differences from the third embodiment will be mainly described.

[0089] The tire sensor 2 of each tire is configured to be able to detect not only the tire pressure and the internal tire temperature, but also the internal tire humidity, which is the relative humidity or absolute humidity of the air inside the tire.

[0090] 14, the air pressure detection unit 21 of the tire sensor 2 includes a pressure sensor 21a, a temperature sensor 21b, and a humidity sensor 21c. The air pressure detection unit 21 outputs a detection signal corresponding to the tire air pressure, a detection signal corresponding to the tire internal temperature Tt, and a detection signal corresponding to the tire internal humidity Th.

[0091] Here, moisture inside a tire has a higher thermal expansion rate than air, so if there is moisture inside the tire, the tire pressure may change due to changes in the water vapor partial pressure caused by the tire internal temperature Tt. For example, when the moisture content inside the tire is high and the humidity inside the tire is high, tire pressure changes are more likely to occur than when the humidity is low.

[0092] Therefore, if the internal humidity Th of each tire is different, the tire pressure of each tire may be different due to the difference. a If the internal tire humidity Th is different between the two, the tire pressure may be different due to the difference. Such changes in tire pressure due to the internal tire humidity Th may reduce the accuracy of determining an abnormal drop in tire pressure due to a tire abnormality.

[0093] In light of this, the pressure correction unit 332 of this embodiment corrects the tire pressure detection value from the pressure detection unit 21 to a reference pressure value, which is the pressure at a predetermined reference temperature and a predetermined reference humidity, based on the tire internal temperature Tt and tire internal humidity Th. As shown in FIG. 15 , when the tire pressure, tire internal temperature Tt, and tire internal humidity Th are input, the pressure correction unit 332 is configured to output a reference pressure value, which is the pressure at the predetermined reference temperature and a predetermined reference humidity. For example, the pressure correction unit 332 refers to a map or a relational expression that defines the relationship between changes in tire internal temperature Tt, changes in tire internal humidity Th, and changes in tire pressure, and converts the tire pressure detection value from the pressure detection unit 21 to a reference pressure value at a predetermined reference temperature and reference humidity.

[0094] Here, the reference humidity is stored in the memory of the second microcomputer 33 together with the reference temperature. The reference humidity is set, for example, to a standard humidity (e.g., 50%) and is set to a common value for each tire. The reference humidity is not limited to a predetermined fixed value, and may be a variable value. The reference humidity may be set to the tire internal humidity Th of any one of the tires on the pressure adjustment date t0 or the average value of the tire internal humidity Th of each tire.

[0095] In the abnormal drop detection process, the vehicle-mounted device 3 calculates the amount of change in air ΔP using the reference pressure value corrected by the pressure correction unit 332. t The abnormal decrease detection process of this embodiment will be described below with reference to Fig. 16. The abnormal decrease detection process shown in Fig. 16 is started, for example, when the tire pressure is adjusted.

[0096] 16, in step S100B, the vehicle-mounted device 3 calculates a reference pressure value for each tire based on the tire pressure, tire internal temperature Tt, and tire internal humidity Th of each tire on the day the tire pressure was adjusted. That is, the vehicle-mounted device 3 corrects the tire pressure detected by the tire pressure detection unit 21 of each tire on the day the tire pressure was adjusted to a reference pressure value that is the pressure at a predetermined reference temperature based on the tire internal temperature Tt and tire internal humidity Th of each tire. Note that in the processing of step S100B, the reference pressure values are calculated for all tires mounted on the vehicle 10, not just the tire whose pressure has been adjusted.

[0097] Next, in step S105B, the on-board device 3 stores the reference pressure value in memory as an initial value P0. The on-board device 3 also acquires, via another ECU, the time when the tire pressure was adjusted as the pressure adjustment date t0.

[0098] Next, in step S110B, the vehicle-mounted device 3 calculates a reference pressure value for each tire based on the tire pressure, tire internal temperature Tt, and tire internal humidity Th of each tire. That is, the vehicle-mounted device 3 corrects the detection value of the tire pressure detection unit 21 for each tire to a reference pressure value, which is the pressure at a predetermined reference temperature and a predetermined reference humidity, based on the tire internal temperature Tt and tire internal humidity Th of each tire. The predetermined reference temperature here is the same as the reference temperature on the day the tire pressure was adjusted. Also, the predetermined reference humidity is the same as the reference humidity on the day the tire pressure was adjusted.

[0099] Next, in step S115B, the vehicle-mounted device 10 converts the reference pressure value obtained in step S110B into the tire pressure "P t Then, in step S120B, the vehicle-mounted device 3 sets the tire air pressures of the wheels 10a to 10d to "P t The warning threshold is set to, for example, the minimum tire pressure specified by regulations.

[0100] On the other hand, the tire air pressure of each wheel 10a to 10d “P t If the tire pressure "P" is equal to or greater than the predetermined warning threshold value, the vehicle-mounted device 3 changes the tire pressure "P" from the initial tire pressure value P0 to the current tire pressure "P" in step S140B. t " to calculate the air pressure change ΔP t That is, the abnormal drop detection unit 331 of the in-vehicle device 3 sets the reference pressure value calculated by the pressure correction unit 332 when the tire pressure was previously adjusted as an initial value P0, and calculates the air pressure change amount ΔP by subtracting the current reference pressure value calculated by the pressure correction unit 332 from the initial value P0. t It is calculated as follows.

[0101] The subsequent processes of steps S150B, S160B, S170B, S180B, S190B, and S200B are the same as the processes of steps S150, S160, S170, S180, S190, and S200 described in the first embodiment, and therefore will not be described again.

[0102] The rest of the configuration is the same as that of the first and third embodiments. The TPMS of this embodiment can obtain the same effects as those of the first and third embodiments, which are achieved by the configurations common to or equivalent to those of the first and third embodiments.

[0103] Furthermore, the TPMS of this embodiment has the following advantages. (1) In this embodiment, the pressure correction unit 332 corrects the tire pressure detected by the pressure detection unit 21 to a reference pressure value, which is the pressure at a reference temperature and humidity, based on the tire internal temperature Tt, which is the temperature inside each tire, and the tire humidity Th. This makes it possible to properly determine abnormal tire pressure drops due to tire abnormalities, since the amount of change in tire pressure is hardly affected by differences in the amount of moisture inside the tire.

[0104] (Other embodiments) Representative embodiments of the present disclosure have been described above, but the present disclosure is not limited to the above-described embodiments and can be modified in various ways, for example, as follows.

[0105] As in the above embodiment, the value detected by the air pressure detection unit 21 when the tire air pressure was previously adjusted is set as the initial value P0, and the value obtained by subtracting the current value detected by the air pressure detection unit 21 from this initial value P0 is the air pressure change amount ΔP t For example, the value detected by the air pressure detection unit 21 on a day prior to the present that is different from the pressure adjustment date t0 is set as the initial value, and the value obtained by subtracting the current value detected by the air pressure detection unit 21 from this initial value is used as the air pressure change amount ΔP t The calculation may be performed as follows.

[0106] As in the above embodiment, the air pressure change amount ΔP t and the reference change ΔP th It is desirable to change the count value X of the leak counter CNT and the judgment threshold value in accordance with the difference between the leak counter CNT and the judgment threshold value, but this is not limitative, and the count value X of the leak counter CNT and the judgment threshold value may be fixed values.

[0107] As in the above embodiment, the air pressure change amount ΔP t is the reference change amount ΔP th It is desirable to reset the leak counter CNT to zero when the air pressure change amount ΔP t is the reference change amount ΔP th If the leak counter CNT is decreased to a value other than zero, or the air pressure change amount ΔP t is the reference change amount ΔP th The leak counter CNT may not be changed even if it falls below this value.

[0108] As in the above embodiment, the air pressure change amount ΔP t is the reference change amount ΔP th It is desirable to count the number of times the air pressure change amount ΔP exceeds the threshold value as a leak counter CNT, and when the leak counter CNT reaches a threshold value, it is determined that an abnormal drop has occurred, but this is not limitative. t is the reference change amount ΔP th If the tire pressure exceeds the threshold, it may be determined that the tire pressure has dropped abnormally.

[0109] The tire sensor 2 and the vehicle-mounted device 3 in the above-described embodiment are configured to be capable of bidirectional communication based on the BLE communication method, but may also be configured to be capable of bidirectional communication based on a communication method other than BLE.

[0110] In the above-described embodiment, the TPMS of the present disclosure is applied to a vehicle 10 having four wheels 10a to 10d, but the TPMS of the present disclosure can also be applied to a vehicle 10 having a greater number of wheels.

[0111] In the above-described embodiments, it goes without saying that the elements constituting the embodiments are not necessarily essential unless they are specifically stated as essential or are clearly considered essential in principle.

[0112] In the above-described embodiments, when numerical values such as the number, values, amounts, ranges, etc. of components of the embodiments are mentioned, they are not limited to the specific numbers unless they are expressly stated as being essential or are clearly limited to a specific number in principle.

[0113] In the above-described embodiments, when referring to the shapes, positional relationships, etc. of components, etc., the shapes, positional relationships, etc. are not limited to those unless otherwise specified or when they are limited in principle to specific shapes, positional relationships, etc.

[0114] The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. The controller and method of the present disclosure may be implemented on a special-purpose computer by configuring a processor with one or more dedicated hardware logic circuits. The controller and method of the present disclosure may be implemented on one or more special-purpose computers configured with a processor and memory programmed to perform one or more functions in combination with a processor configured with one or more hardware logic circuits. The computer program may also be stored on a computer-readable non-transitory tangible storage medium as instructions executed by a computer. [Explanation of symbols]

[0115] 10 vehicles 10a~10d wheels 11 Body 2 Tire Sensors 21 Air pressure detection unit 331 Abnormal drop detection unit

Claims

1. A tire pressure monitoring system applied to a vehicle (10) having a body (11) and a plurality of wheels (10a, 10b, 10c, 10d) including tires attached thereto, a tire sensor (2) including an air pressure detection unit (21) for detecting tire air pressures of the plurality of wheels; an abnormal decrease detection unit (331) that detects an abnormal decrease in tire air pressure caused by an abnormality in the tire, the abnormal drop detection unit calculates the amount of change in the value detected by the air pressure detection unit over a predetermined period as an amount of change in air pressure, and determines whether or not there is an abnormal drop in air pressure based on a comparison between the amount of change in air pressure and a predetermined reference amount of change; The abnormal drop detection unit sets the reference change amount based on the smallest change amount of the air pressures of the plurality of wheels.

2. a pressure correction unit (332) that corrects the tire pressure detection value detected by the tire pressure detection unit to a reference pressure value that is the pressure at a predetermined reference temperature based on a tire internal temperature that is the temperature inside the tire; the predetermined period is a period from the previous adjustment of the tire pressure of at least one of the plurality of tires to the present; 2. The tire pressure monitoring system according to claim 1, wherein the abnormal drop detection unit sets the reference pressure value calculated by the pressure correction unit when the tire pressure was last adjusted as an initial value, and calculates the amount of change in tire pressure by subtracting the current reference pressure value calculated by the pressure correction unit from the initial value.

3. 3. The tire pressure monitoring system according to claim 2, wherein the pressure correction unit corrects the tire pressure detected by the tire pressure detection unit to the reference pressure value at the reference temperature and a predetermined reference humidity based on the tire internal temperature and humidity.

4. the predetermined period is a period from the previous adjustment of the tire pressure of at least one of the plurality of tires to the present; 2. The tire pressure monitoring system according to claim 1, wherein the abnormal drop detection unit sets the detection value of the tire pressure detection unit when the tire pressure was last adjusted as an initial value, and calculates the amount of change in tire pressure by subtracting the current detection value of the tire pressure detection unit from the initial value.

5. A tire pressure monitoring system applied to a vehicle (10) having a body (11) and a plurality of wheels (10a, 10b, 10c, 10d) including tires attached thereto, a tire sensor (2) including an air pressure detection unit (21) for detecting tire air pressures of the plurality of wheels; an abnormal decrease detection unit (331) that detects an abnormal decrease in tire air pressure caused by an abnormality in the tire, the abnormal drop detection unit calculates the amount of change in the value detected by the air pressure detection unit over a predetermined period as an amount of change in air pressure, and determines whether or not the abnormal drop has occurred based on a comparison between the amount of change in air pressure and a predetermined reference amount of change; The abnormal drop detection unit counts the number of times the air pressure change amount exceeds the reference change amount as a leak counter, and determines that the air pressure has dropped abnormally when the leak counter reaches a determination threshold.

6. 6. The tire pressure monitoring system according to claim 5, wherein the abnormal drop detection unit sets the reference change amount based on the smallest change amount of the air pressures of the plurality of wheels.

7. 6. The tire pressure monitoring system according to claim 5, wherein the abnormal drop detection unit sets the reference change amount based on an amount of change in the tire pressure during the predetermined period estimated from tire pressure data in which a relationship between the elapsed time after the tire pressure adjustment and the amount of change in the tire pressure is defined.

8. 8. The tire pressure monitoring system according to claim 5, wherein the abnormal drop detection unit increases the count value added to the leak counter as the difference between the amount of change in tire pressure and the reference amount of change increases.

9. 8. The tire pressure monitoring system according to claim 5, wherein the abnormal drop detection unit reduces the determination threshold value as the difference between the amount of change in tire pressure and the reference amount of change increases.

10. 10. The tire pressure monitoring system according to claim 5, wherein the abnormal drop detection unit resets the leak counter to zero when the amount of change in air pressure becomes equal to or less than the reference amount of change.

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