Tire air pressure monitoring system

Abstract

To appropriately monitor a tire air pressure, while suppressing dark current in an off state in which a switch capable of making a vehicle travelable is turned off.SOLUTION: A tire air pressure monitoring system includes sensor units 2a to 2d, and an on-vehicle machine 3. The on-vehicle machine 3 determines a change amount of a tire air pressure per predetermined time, in an off state in which a switch making a vehicle 1 travelable is turned off, as an attenuation factor α. The on-vehicle machine 3 changes a reception period of a frame transmitted from the sensor units 2a to 2d so that the smaller the attenuation factor α is made, the smaller the reception frequency of the frame is made.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a tire pressure monitoring system for monitoring tire pressure.

Background Art

[0002] Conventionally, as a tire pressure monitoring system (hereinafter referred to as TPMS), there is known one that continues to receive radio waves on the in-vehicle unit side during a period until the change in tire pressure subsides after the IG switch is turned off (see, for example, Patent Document 1). In Patent Document 1, although radio waves are received on the in-vehicle unit side while the IG switch is off, the period is limited to until the change in tire pressure subsides after the IG switch is turned off, thereby suppressing an increase in dark current. Note that TPMS is an abbreviation for Tire Pressure Monitoring System.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As described above, in the TPMS described in Patent Document 1, when the change in tire pressure falls within a predetermined range, the reception of radio waves on the in-vehicle unit side is stopped, and thereafter, the change in tire pressure cannot be acquired. For this reason, even if the dark current in the off state where the switch for making the vehicle drivable is turned off can be suppressed, it is difficult to appropriately monitor the tire pressure.

[0005] An object of the present disclosure is to appropriately monitor tire pressure while suppressing dark current in an off state where the switch for making the vehicle drivable is turned off.

Means for Solving the Problems

[0006] The invention according to claim 1 is a tire air pressure monitoring system applied to a vehicle (1) having a plurality of wheels (5a to 5d) including tires, a sensor unit (2a to 2d) that outputs a detection signal regarding the tire air pressure of the wheel, generates transmission data regarding the tire air pressure based on the detection signal, and transmits a frame in which the transmission data is stored at a predetermined period; an in-vehicle unit (3) provided on the vehicle body (6) of the vehicle, which receives the frame and detects the tire air pressure from the transmission data stored in the frame, In the off state where the switch for making the vehicle drivable is turned off, the in-vehicle unit obtains the amount of change in tire air pressure per predetermined time as the attenuation rate, and changes the reception period of the frame so that the reception frequency of the frame transmitted from the sensor unit decreases as the attenuation rate decreases.

[0007] Thus, if the configuration is such that the reception period of the frame is changed according to the attenuation rate of the tire air pressure, it is possible to continue receiving the frame from the sensor unit while suppressing the dark current in the off state of the switch for making the vehicle drivable.

[0008] Note that the reference signs with parentheses attached to each component etc. show an example of the correspondence relationship between the component etc. and the specific components etc. described in the embodiments described later.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0010] 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 may be given the same reference numerals, and the description thereof may be omitted. Further, in the embodiments, when only a part of the components is described, the components described in the preceding embodiments can be applied to other parts of the components. The following embodiments can be partially combined with each other as long as there is no problem in the combination, even if not particularly specified.

[0011] (First Embodiment) This embodiment will be described with reference to FIGS. 1 to 8. In this embodiment, an example in which the TPMS of the present disclosure is applied to a vehicle 1 having four wheels 5a to 5d will be described. Note that the upward direction on the paper surface of FIG. 1 is the front of the vehicle 1, the downward direction on the paper surface is the rear of the vehicle 1, and the left and right directions on the paper surface are the left and right directions of the vehicle 1. Further, when the four wheels 5a to 5d are separately described, the four wheels 5a to 5d may be denoted as the left front wheel FL, the right front wheel FR, the left rear wheel RL, and the right rear wheel RR.

[0012] The TPMS shown in FIG. 1 includes sensor units 2a to 2d, an in-vehicle unit 3, and a display device 4. The display device 4 may be configured as a dedicated device for the TPMS, or may be configured as a device shared with a meter, a navigation system, or the like.

[0013] As shown in FIG. 1, the sensor units 2a to 2d are attached to the respective wheels 5a to 5d of the vehicle 1, and detect the air pressure and temperature of the tires attached to the wheels 5a to 5d. Then, the sensor units 2a to 2d store, as transmission data, the data of the detection signal indicating the detection result such as the tire air pressure in a frame and transmit it. Further, the in-vehicle unit 3 is attached to the vehicle body 6 side of the vehicle 1, receives the frame transmitted from the sensor units 2a to 2d, and detects the tire air pressure based on the transmission data stored therein. Also, the sensor units 2a to 2d and the in-vehicle unit 3 according to the present embodiment are configured to be able to communicate from the sensor units 2a to 2d to the in-vehicle unit 3. In the TPMS of the present embodiment, the sensor units 2a to 2d function as a "transmitter" and the in-vehicle unit 3 functions as a "receiver". Note that the sensor units 2a to 2d and the in-vehicle unit 3 may be configured to perform two-way communication that is possible not only from the sensor units 2a to 2d to the in-vehicle unit 3 but also vice versa.

[0014] Hereinafter, with reference to FIGS. 2 and 3, the detailed configurations of the sensor units 2a to 2d and the in-vehicle unit 3 that constitute the TPMS of the present embodiment will be described.

[0015] As shown in FIG. 2, the sensor units 2a to 2d are configured to include a detection unit 21, a sensor control unit 22, a sensor communication unit 23, a battery 24, and an antenna 25, and each unit is driven based on the power supply from the battery 24.

[0016] The detection unit 21 is configured to include, for example, a pressure sensor 21a, a temperature sensor 21b, and an acceleration sensor 21c. The pressure sensor 21a outputs a detection signal corresponding to the tire air pressure. The temperature sensor 21b outputs a detection signal corresponding to the tire internal temperature. The acceleration sensor 21c outputs a detection signal corresponding to the acceleration generated with the rotation of the tire, for example, the acceleration in the radial direction of each of the wheels 5a to 5d. Then, the detection unit 21 transmits the detection signals output from these pressure sensor 21a, temperature sensor 21b, and acceleration sensor 21c to the sensor control unit 22. Among these, the detection signal corresponding to the tire air pressure and the detection signal corresponding to the tire internal temperature are used for tire air pressure detection, and the detection signal corresponding to the acceleration is used for detecting that the vehicle 1 is in motion.

[0017] The sensor control unit 22 is configured by a microcomputer including a CPU, a ROM, a RAM, an I / O, etc., and executes predetermined processing according to a program stored in the ROM or the like. The sensor control unit 22 stores ID information including sensor unit unique identification information for identifying each of the sensor units 2a to 2d and vehicle unique identification information for identifying the host vehicle.

[0018] The sensor control unit 22 receives the detection signal output from the detection unit 21, processes the signal, and processes it as necessary. Then, the sensor control unit 22 stores, in a frame, data indicating the detection results of the tire air pressure and the tire internal temperature used for tire air pressure detection, together with the ID information of each of the sensor units 2a to 2d, and sends the frame to the sensor communication unit 23 at a predetermined periodic transmission interval. In the following description, the data indicating the detection results of the tire air pressure and the tire internal temperature is referred to as detection data related to the tire air pressure.

[0019] The sensor communication unit 23 functions as an output unit that transmits, via the antenna 25, the frame sent from the sensor control unit 22 toward the in-vehicle unit 3 as RF waves. Here, the sensor communication unit 23 performs transmission and reception using, for example, radio waves in the UHF band of 300 MHz or 400 MHz, but the frequency band of the radio waves to be used can be arbitrarily selected.

[0020] The battery 24 supplies power to the detection unit 21, the sensor control unit 22, etc. Receiving the power supply from the battery 24, data collection regarding the tire air pressure at the detection unit 21 and various calculations at the sensor control unit 22 are executed.

[0021] The sensor units 2a to 2d configured in this way are attached, for example, to the air injection valves in the wheels of each wheel 5a to 5d and are arranged such that the detection unit 21 is exposed to the inside of the tire. As a result, the sensor units 2a to 2d detect the tire air pressure of the corresponding wheel and transmit a frame at a predetermined timing through the antenna 25 provided in each sensor unit 2a to 2d.

[0022] On the other hand, as shown in FIG. 3, the in-vehicle unit 3 has a configuration including an antenna 31, an in-vehicle communication unit 32, and an in-vehicle control unit 33. The in-vehicle unit 3 is driven by power supplied from the battery BT mounted on the vehicle 1.

[0023] The antenna 31 is provided on the vehicle body 6 and is for receiving the frames sent from each of the sensor units 2a to 2d. Here, the antenna 31 is configured as a single common antenna that comprehensively communicates with each of the sensor units 2a to 2d, but it may be provided for each of the sensor units 2a to 2d.

[0024] When the frame transmitted from each of the sensor units 2a to 2d is received by the antenna 31, the in-vehicle communication unit 32 functions as an input unit that demodulates it and sends it to the in-vehicle control unit 33.

[0025] The in-vehicle control unit 33 is composed of a microcomputer including a CPU, a memory M such as a ROM and a RAM, an I / O, etc., and executes various processes according to the programs stored in the memory M. Specifically, the in-vehicle control unit 33 operates based on the power supply from the battery BT, controls the frame reception in the in-vehicle communication unit 32, and performs various processes related to tire air pressure detection.

[0026] For example, as various processes related to tire air pressure detection, the in-vehicle control unit 33 performs warning determination processing, etc. as the specified processing of the TPMS.

[0027] In the warning determination processing, various signal processes and calculations are performed based on the detection data related to the tire air pressure stored in the frame received from the in-vehicle communication unit 32, and an electrical signal corresponding to the tire air pressure is output to the display device 4. In the warning determination processing, for example, the tire air pressure is compared with a predetermined warning threshold value, and when it is detected that the tire air pressure has dropped below the predetermined warning threshold value P TH below, a signal to that effect is output to the display device 4. Also, when the tire air pressure is detected by the sensor units 2a to 2d, based on the data indicating that a tire air pressure drop has occurred included in the received frame, it is also possible to notify the display device 4 that a tire air pressure drop has occurred.

[0028] Furthermore, when the in-vehicle control unit 33 has obtained the tire air pressure of each of the four wheels 5a to 5d, it can also output the tire air pressure to the display device 4 in correspondence with each of the wheels 5a to 5d. In the memory M of the in-vehicle control unit 33, the ID information of the sensor units 2a to 2d arranged on each of the wheels 5a to 5d is stored in association with the positions of each of the wheels 5a to 5d. Therefore, the in-vehicle control unit 33 collates with the ID information stored in the frame, recognizes which of the sensor units 2a to 2d the received frame is attached to among the wheels 5a to 5d, and can identify the wheels 5a to 5d with a decreased tire air pressure. Based on this, when a decrease in tire air pressure occurs, the in-vehicle control unit 33 identifies the wheels 5a to 5d with the decreased tire air pressure and outputs the information to the display device 4. Also, even when no decrease in tire air pressure has occurred, the obtained tire air pressure may be output to the display device 4 in correspondence with each of the wheels 5a to 5d.

[0029] In this way, it is notified to the driver that the tire air pressure of any one of the four wheels 5a to 5d has decreased, or the tire air pressure of each of the four wheels 5a to 5d is transmitted to the display device 4.

[0030] As shown in FIG. 1, the display device 4 is arranged at a location visible to the driver and is constituted by, for example, an alarm lamp or a display installed in the instrument panel of the vehicle 1. When a signal indicating that the tire air pressure has decreased is sent from the in-vehicle control unit 33 in the in-vehicle unit 3 to the display device 4, the display device 4 notifies the driver of the decrease in tire air pressure by displaying the message. Alternatively, when the tire air pressure of each of the four wheels 5a to 5d is transmitted from the in-vehicle unit 3, the display device 4 displays each tire air pressure in correspondence with each of the wheels 5a to 5d.

[0031] In this embodiment, the display device 4 is used as a warning unit for warning the driver. However, in addition to the display device 4 that gives a visual warning, a device that gives an audible warning, such as a speaker, may be used as the warning unit.

[0032] The in-vehicle unit 3 configured as described above is connected to other in-vehicle devices including the DCM 7 via a communication network built in the vehicle 1 such as CAN. The DCM 7 is a vehicle communication module and can communicate information with a communication center by wireless communication. Note that CAN is an abbreviation for Controller Area Network. Also, DCM is an abbreviation for Data Communication Module.

[0033] The in-vehicle unit 3 can, for example, receive requests from information terminals SD such as tablets and smartphones owned by the user via a communication center or the like using the DCM 8. Also, the in-vehicle unit 3 can transmit detection data and abnormal data related to tire pressure to the information terminal SD.

[0034] In the TPMS configured as described above, information regarding tire pressure is notified from the sensor units 2a to 2d to the in-vehicle unit 3 by periodic frame transmission. This notification is carried out regardless of the on / off state of the activation switch. Note that the activation switch is a switch for enabling the vehicle 1 to run. The activation switch corresponds to, for example, an ignition switch (i.e., an IG switch) in an engine-equipped vehicle and a switch corresponding to a power switch in an electric vehicle.

[0035] In the in-vehicle unit 3, when the activation switch of the vehicle 1 is in the on state, frame reception is carried out in accordance with the frame transmission frequency of the sensor units 2a to 2d so that frames from the sensor units 2a to 2d can be received.

[0036] On the other hand, even when the activation switch of the vehicle 1 is in the off state, it is conceivable that the in-vehicle unit 3 carries out frame reception in accordance with the frame transmission frequency of the sensor units 2a to 2d. However, there is a risk that the vehicle 1 may not be able to start due to an increase in the standby current of the battery BT.

[0037] On the other hand, in the prior art, although radio waves are received on the in-vehicle unit 3 side while the activation switch is off, there is a technology that suppresses an increase in dark current by limiting the period until the change in tire pressure subsides after the activation switch is turned off.

[0038] According to this, although the dark current in the off state where the activation switch is off can be suppressed, when the change in tire pressure falls within a predetermined range, frame reception on the in-vehicle unit 3 side stops, making it difficult to appropriately monitor the tire pressure.

[0039] Taking these into consideration, the TPMS of the present embodiment changes the reception cycle of frames transmitted from the sensor units 2a to 2d according to the amount of change in tire pressure per predetermined time in the off state where the activation switch is off.

[0040] Specifically, the in-vehicle unit 3 obtains the amount of change in tire pressure per predetermined time in the off state of the activation switch as the "attenuation rate α". For example, as shown in FIG. 4, the in-vehicle unit 3 obtains the "attenuation rate α" as a value obtained by dividing the difference between the tire pressure Prx2 received this time and the tire pressure Prx1 received last time from the sensor units 2a to 2d by the reception cycle (= t2 - t1).

[0041] Then, the in-vehicle unit 3 sets the reception cycle of frames from the sensor units 2a to 2d according to the attenuation rate α. Specifically, the in-vehicle unit 3 changes the reception cycle of frames so that the reception frequency of frames transmitted from the sensor units 2a to 2d becomes lower as the attenuation rate α becomes smaller. For example, as shown in FIG. 5, the in-vehicle unit 3 obtains the reception cycle of frames from the attenuation rate α using a function or control map in which the relationship between the attenuation rate α and the reception cycle of frames is defined in advance. Note that the relationship between the attenuation rate α and the reception cycle of frames may be such that the reception cycle of frames changes continuously according to the attenuation rate α as shown in FIG. 5, or may be such that the reception cycle of frames changes stepwise according to the attenuation rate α.

[0042] Next, the flow of the specific tire pressure monitoring process executed by the in-vehicle device 3 of the present embodiment will be described with reference to FIG. 6. The process shown in FIG. 6 is periodically or irregularly executed by the in-vehicle control unit 33 of the in-vehicle device 3.

[0043] As shown in FIG. 6, in step S100, the in-vehicle control unit 33 determines whether the start switch is in the ON state. If the start switch is in the ON state, the in-vehicle control unit 33 proceeds to step S110, and if the start switch is in the OFF state, the in-vehicle control unit 33 proceeds to step S130.

[0044] When the start switch is in the ON state, in step S110, the in-vehicle control unit 33 performs reception processing of frames periodically transmitted from each sensor unit 2a to 2d. The in-vehicle control unit 33 basically continuously performs reception processing so as to be able to receive frames from each sensor unit 2a to 2d.

[0045] After that, when the in-vehicle control unit 33 receives a frame from each sensor unit 2a to 2d, it proceeds to step S120 and performs the above-described alarm determination and display on the display device 4 as the specified processing of the TPMS.

[0046] On the other hand, when the start switch is in the OFF state, in step S130, the in-vehicle control unit 33 determines whether it is the intermittent reception timing. Specifically, the in-vehicle control unit 33 determines whether the reception cycle for receiving a frame from each sensor unit 2a to 2d has arrived.

[0047] If the in-vehicle control unit 33 determines that it is the intermittent reception timing, it proceeds to step S140 and performs reception processing of frames transmitted from each sensor unit 2a to 2d. As a result, the in-vehicle control unit 33 intermittently receives frames from each sensor unit 2a to 2d. If it is not the intermittent reception timing, the in-vehicle control unit 33 exits this process.

[0048] Subsequently, in step S150, the in-vehicle control unit 33 determines whether the tire pressure is greater than the warning threshold value P TH using the information stored in the frame. Specifically, the in-vehicle control unit 33 compares the tire pressure included in the frame with the warning threshold value P TH stored in the memory M to determine whether the tire pressure is greater than the warning threshold value P TH . The warning threshold value P TH is set, for example, to a value 10 - 20% lower than the specified pressure of the tire. Note that the warning threshold value P TH is preferably configured to be arbitrarily settable by the user, but may also be a fixed value.

[0049] If the tire pressure is greater than the warning threshold value P TH , in step S160, the in-vehicle control unit 33 sets, as a determination threshold value, a value obtained by adding a predetermined margin value Px to the warning threshold value P TH and determines whether the tire pressure is greater than the determination threshold value.

[0050] The margin value Px is set to grasp whether the tire pressure is in a state sufficiently greater than the warning threshold value P TH or in a state immediately before reaching the warning threshold value P TH . The margin value Px is set as a margin to prevent the warning threshold value P TH from being exceeded due to pressure error or external influence. The margin value Px is set, for example, to a value smaller than a value obtained by subtracting the warning threshold value P TH from the specified pressure of the tire.

[0051] If the tire pressure is greater than the determination threshold value, it is assumed that the tire pressure is sufficiently high with respect to the warning threshold value P TH and it is difficult to become an abnormal state in a short time. Therefore, if the tire pressure is greater than the determination threshold value, in step S170, the in-vehicle control unit 33 calculates the attenuation rate α.

[0052] Specifically, the in-vehicle control unit 33 calculates the attenuation rate α as the value obtained by dividing the difference between the tire air pressure Prx2 received this time and the tire air pressure Prx1 received last time by the reception period (= t2 - t1).

[0053] Here, since the tire air pressure changes according to the temperature of the tire, the attenuation rate α also changes according to the temperature of the tire. For this reason, it is desirable that the in-vehicle control unit 33 performs temperature correction to convert the tire air pressure Prx received from each sensor unit 2a to 2d into the pressure at the reference temperature, and obtains the attenuation rate α using the temperature-corrected tire air pressure Prx.

[0054] Subsequently, in step S180, the in-vehicle control unit 33 sets the reception period of the frames transmitted from each sensor unit 2a to 2d to a value according to the attenuation rate α. Specifically, as shown in FIGS. 7 and 8, the in-vehicle control unit 33 changes the reception period of the frames so that the reception frequency of the frames transmitted from the sensor units 2a to 2d decreases as the attenuation rate α decreases. In other words, the in-vehicle control unit 33 changes the reception period of the frames so that the reception frequency of the frames transmitted from the sensor units 2a to 2d increases as the attenuation rate α increases.

[0055] On the other hand, when the tire air pressure is equal to or lower than the determination threshold value, there is a concern that the tire air pressure is close to the warning threshold value P TH and may become abnormal in a short time. For this reason, when the tire air pressure is equal to or lower than the determination threshold value, the in-vehicle control unit 33 changes the reception period of the frames so that the reception frequency of the frames decreases regardless of the attenuation rate α in step S190. Specifically, as shown in FIGS. 7 and 8, the in-vehicle control unit 33 sets the reception period of the frames transmitted from the sensor units 2a to 2d to a certain short period (for example, about 1 h) regardless of the attenuation rate α.

[0056] Here, when the tire pressure is equal to or lower than the determination threshold value, the reception cycle is set within a range that is equal to or longer than the reception cycle when the tire pressure is higher than the determination threshold value and shorter than the reception cycle in the ON state of the activation switch. When the tire pressure is equal to or lower than the determination threshold value, the reception cycle is set, for example, to the minimum cycle of the reception cycle when the tire pressure is higher than the determination threshold value.

[0057] Also, when the tire pressure is equal to or lower than the warning threshold value P TH hereinafter, the in-vehicle control unit 33 proceeds to step S200 and notifies the user of the abnormality of the tire pressure. Specifically, the in-vehicle control unit 33 outputs an abnormality signal indicating the abnormality of the tire pressure to the outside so that the user can recognize the abnormality of the tire pressure.

[0058] Here, when the activation switch is in the OFF state, there may be a case where the user is not on board the vehicle 1. For this reason, it is desirable that the in-vehicle control unit 33 transmits an abnormality signal indicating the abnormality of the tire pressure to the information terminal SD such as a tablet or a smartphone owned by the user via the DCM7.

[0059] The TPMS described above obtains the amount of change in tire pressure per predetermined time as the attenuation rate α in the OFF state where the activation switch is turned off. Then, the TPMS changes the reception cycle of the frame so that the smaller the attenuation rate α, the smaller the reception frequency of the frame transmitted from each sensor unit 2a to 2d. With such a configuration that changes the reception cycle of the frame according to the attenuation rate α of the tire pressure, it is possible to continue receiving the frames from each sensor unit 2a to 2d while suppressing the dark current in the OFF state of the activation switch that enables the vehicle 1 to run. As a result, over-discharge of the battery BT due to monitoring of the tire pressure can be suppressed.

[0060] Also, the TPMS of the present embodiment has the following features.

[0061] (1) When the tire pressure in the off state of the ignition switch is greater than a predetermined determination threshold value, in-vehicle unit 3 changes the reception cycle of the frame so that the reception frequency of the frames transmitted from each sensor unit 2a to 2d becomes smaller as the attenuation rate α becomes smaller. Further, when the tire pressure in the off state of the ignition switch becomes equal to or lower than the determination threshold value, in-vehicle unit 3 changes the reception cycle of the frame so that the reception frequency of the frame becomes larger regardless of the magnitude of the attenuation rate α.

[0062] When the tire pressure is greater than the determination threshold value and there is a margin until an abnormality occurs in the tire pressure, even if the frequency of obtaining the tire pressure is small, it is unlikely to cause a problem. For this reason, when the tire pressure is greater than the determination threshold value, it is desirable to change the reception cycle of the frame so that the reception frequency of the frames from the sensor units 2a to 2d becomes smaller as the attenuation rate α of the tire pressure becomes smaller.

[0063] On the other hand, when the tire pressure is equal to or lower than the determination threshold value, since the possibility of an abnormality occurring in the tire pressure increases, it is desirable to change the reception cycle of the frame so that the reception frequency of the frames from the sensor units 2a to 2d becomes larger regardless of the attenuation rate α of the tire pressure.

[0064] (2) When the tire pressure in the off state of the ignition switch becomes equal to or lower than the determination threshold value, in-vehicle unit 3 changes the reception cycle of the frame so that the reception frequency of the frame becomes larger regardless of the magnitude of the attenuation rate α. When the tire pressure is low, since the possibility of an abnormality occurring in the tire pressure increases, it is desirable to change the reception cycle of the frame so that the reception frequency of the frames transmitted from the sensor units 2a to 2d becomes larger regardless of the attenuation rate α of the tire pressure.

[0065] (3) The determination threshold value is set to a value obtained by adding a predetermined margin value Px to the warning threshold value P TH required for notification to the user. According to this, when the tire pressure is the warning threshold value P THSince the reception frequency of the frames transmitted from the sensor units 2a to 2d increases from the stage before dropping to the lowest level, it becomes possible to detect an abnormality in the tire air pressure at an early stage.

[0066] (4) When the tire air pressure in the off state of the ignition switch is lower than the alarm threshold value P TH the in-vehicle device 3 outputs an abnormal signal indicating the abnormality of the tire air pressure to the outside so that the user can recognize the abnormality of the tire air pressure. According to this, it becomes possible to detect an abnormality in the tire air pressure at an early stage.

[0067] (Second Embodiment) Next, the second embodiment will be described with reference to FIG. 9. In this embodiment, the parts different from the first embodiment will be mainly described.

[0068] In the TPMS of this embodiment, among the tire air pressure monitoring processes executed by the in-vehicle device 3, the process when the tire air pressure in the off state of the ignition switch is lower than the alarm threshold value P TH is different from that of the first embodiment.

[0069] Hereinafter, the flow of the monitoring process executed by the in-vehicle device 3 of this embodiment will be described with reference to FIG. 9. Since the processes from step S100 to S200 shown in FIG. 9 are the same as the processes from step S100 to S200 described in the first embodiment, the description thereof will be omitted.

[0070] As shown in FIG. 9, the in-vehicle control unit 33 of this embodiment shifts to step S210 after notifying the user of the abnormality of the tire air pressure in step S200. In step S210, the in-vehicle control unit 33 stops the intermittent reception of the frames transmitted from the sensor units 2a to 2d.

[0071] The in-vehicle control unit 33 stops the intermittent reception of frames, for example, by setting a flag for negating the determination process in step S130. Note that the in-vehicle control unit 33 may be configured to set the reception cycle of frames to a maximum value that is not normally set so that the intermittent reception of frames is substantially stopped. Note that it is desirable that the in-vehicle control unit 33 stops the reception of frames while the start switch is off in order to suppress dark current, and resumes the reception of frames when the start switch is switched to the on state.

[0072] For other aspects, they are the same as those in the first embodiment. The TPMS of this embodiment can obtain the same effects as those achieved by the common configuration or equivalent configuration as that of the first embodiment in the same manner as the first embodiment.

[0073] In addition, the TPMS of this embodiment has the following features.

[0074] (1) After the in-vehicle device 3 outputs an abnormal signal indicating an abnormality in the tire air pressure to the outside, it stops receiving frames transmitted from the sensor units 2a to 2d. According to this, it is possible to suppress the dark current in the off state of the start switch.

[0075] (Other embodiments) As described above, the representative embodiments of the present disclosure have been described. However, the present disclosure is not limited to the above-described embodiments, and can be variously modified, for example, as follows.

[0076] In the above-described embodiment, the sensor units 2a to 2d have been described by taking as an example those attached to the air injection valve, but they may be provided in other locations. As an example, they may be in a form attached instead of the valve cap, or in a form attached on the tread inside the tire.

[0077] In the above-described embodiment, an example in which the sensor units 2a to 2d are provided for all of the wheels 5a to 5d has been shown, but the present disclosure can be applied to a TPMS provided for at least one of them.

[0078] As in the above-described embodiment, in the OFF state of the activation switch, it is desirable that the reception cycle of the frame be changed according to the comparison result between the tire air pressure and the determination threshold value, but it is not necessary to be so.

[0079] Further, the determination threshold value is preferably set to a value obtained by adding a predetermined margin value Px to the warning threshold value P TH required for notification to the user, but it is not necessary to be so. The determination threshold value may be set to, for example, the warning threshold value P TH For example, the determination threshold value may not be a fixed value, and may be set to a larger value as the attenuation rate α is larger.

[0080] As in the above-described embodiment, it is desirable that the in-vehicle device 3 outputs an abnormal signal to the outside when the tire air pressure in the OFF state of the activation switch is lower than the warning threshold value P TH but it is not necessary to be so. The in-vehicle device 3 may, for example, display an abnormality in the tire air pressure on the display device 4 at the timing when the user gets in the vehicle or at the next activation.

[0081] In the above-described embodiment, the part provided on the vehicle body 6 side of the TPMS is collectively described as the in-vehicle device 3, but the in-vehicle device 3 does not necessarily have to be a single configuration. For example, the antenna 31 and the in-vehicle communication unit 32 that perform the transmission and reception functions and the in-vehicle control unit 33 that performs the tire air pressure detection function may be provided at separate locations.

[0082] In the above-described embodiment, it goes without saying that the elements constituting the embodiment are not necessarily essential except in cases where it is explicitly stated that they are particularly essential and cases where they are considered to be clearly essential in principle.

[0083] In the above-described embodiment, when numerical values such as the number, numerical value, quantity, range, etc. of the components of the embodiment are mentioned, they are not limited to the specific number except in cases where it is explicitly stated that they are particularly essential and cases where they are clearly limited to a specific number in principle.

[0084] In the above embodiments, when referring to the shape, positional relationship, etc. of components and the like, unless specifically specified or limited to a specific shape, positional relationship, etc. in principle, it is not limited to such shape, positional relationship, etc.

[0085] The control unit and its method of the present disclosure may be implemented by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied by a computer program. The control unit and its method of the present disclosure may be implemented by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. The control unit and its method of the present disclosure may be implemented by one or more dedicated computers configured by a combination of a processor and a memory programmed to execute one or more functions and a processor configured by one or more hardware logic circuits. Further, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions to be executed by a computer.

Description of Reference Numerals

[0086] 1 Vehicle 2a to 2d Sensor unit 3 On-vehicle device 5a to 5d Wheel 6 Vehicle body

Claims

1. A tire air pressure monitoring system applied to a vehicle (1) having a plurality of wheels (5a to 5d) including tires, a sensor unit (2a to 2d) that outputs a detection signal related to the tire air pressure of the wheel, generates transmission data related to the tire air pressure based on the detection signal, and transmits a frame storing the transmission data at a predetermined period; and an in-vehicle device (3) provided on a vehicle body (6) of the vehicle, receiving the frame, and detecting the tire air pressure from the transmission data stored in the frame. The in-vehicle device obtains, as a decay rate, a change amount of the tire air pressure per predetermined time in an off state where a switch for enabling the vehicle to travel is turned off, and changes a reception period of the frame so that a reception frequency of the frame transmitted from the sensor unit becomes smaller as the decay rate becomes smaller. A tire air pressure monitoring system.

2. The in-vehicle device, when the tire air pressure in the off state is greater than a predetermined determination threshold value, changes the reception period of the frame so that the reception frequency of the frame transmitted from the sensor unit becomes smaller as the decay rate becomes smaller, when the tire air pressure in the off state becomes equal to or less than the determination threshold value, changes the reception period of the frame so that the reception frequency of the frame becomes larger regardless of the magnitude of the decay rate. The tire air pressure monitoring system according to claim 1.

3. The in-vehicle device changes the reception period of the frame so that the reception frequency of the frame transmitted from the sensor unit becomes smaller as the decay rate becomes smaller when the tire air pressure in the off state is greater than a predetermined determination threshold value. The tire air pressure monitoring system according to claim 1.

4. The in-vehicle device changes the reception period of the frame so that the reception frequency of the frame becomes larger regardless of the magnitude of the decay rate when the tire air pressure in the off state becomes equal to or less than the determination threshold value. The tire air pressure monitoring system according to claim 3.

5. The determination threshold value is set to a value obtained by adding a predetermined margin value to an alarm threshold value for which notification to a user is required. The tire air pressure monitoring system according to any one of claims 2 to 4.

6. The in-vehicle device according to claim 5 outputs an abnormal signal indicating the abnormality of the tire air pressure to the outside so that the user can recognize the abnormality of the tire air pressure when the tire air pressure in the off state is lower than the warning threshold value.

7. The in-vehicle device according to claim 6 stops receiving the frame transmitted from the sensor unit after outputting the abnormal signal to the outside.

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