JP2012240499A - Tire pneumatic pressure monitoring system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electric power consumption in a tire pneumatic pressure monitoring system.SOLUTION: When receiving a trigger signal St, sensor units 30a-30d transmit an information signal Si only at transmission frequency designated by the trigger signal St, and then, complete transmission of the information signal Si. Thus, even if the sensor units 30a-30d of a vehicle receive a trigger signal St from another vehicle unintentionally, the information signal Si is not continuously transmitted. Since transmission frequency of the information signal Si is determined based on transmission frequency information included in the trigger signal St, reception frequency of the trigger signal St as well as frequency of signal processing in the sensor units 30a-30d can be reduced.

Description

  The present invention relates to a tire pressure monitoring system.

  Conventionally, a tire pressure monitoring system (TPMS: Tire Pressure Monitoring System) that monitors tire pressure is known. Each tire of a vehicle on which the TPMS is mounted is provided with a sensor unit that detects the tire air pressure. Each sensor unit transmits an information signal including tire pressure information detected at regular intervals to the receiver. When it is determined that the tire pressure is equal to or lower than the threshold value based on the received information signal, the receiver warns the user through an indicator.

  In the said structure, since an information signal is transmitted for every fixed period even during a stop, it is unpreferable from a viewpoint of consumption of the battery power in a sensor unit. Therefore, for example, in the TPMS described in Patent Document 1, the vehicle is provided with an initiator corresponding to the sensor unit. The initiator wirelessly transmits a trigger signal at regular intervals to the sensor unit only during traveling. When the sensor unit receives the trigger signal, the sensor unit transmits an information signal. As a result, it is possible to eliminate the transmission of the information signal while the vehicle is stopped and the power consumption required for the transmission.

JP 2010-221768 A

  The sensor unit in Patent Document 1 needs to perform signal processing such as reception and demodulation of a trigger signal at regular intervals. This is not preferable from the viewpoint of battery power consumption. Therefore, a configuration is conceivable in which the sensor unit starts transmission of an information signal every fixed period once receiving a trigger signal, and thereafter ends transmission of the information signal when receiving an end signal. In this configuration, it is possible to reduce the signal processing of the trigger signal and thus the power consumption related thereto.

  However, when the traveling vehicle unintentionally receives a trigger signal from another traveling vehicle, the sensor unit continues to transmit an information signal at regular intervals. Also in this case, battery power is consumed.

As described above, there has been a demand for a TPMS capable of suppressing power consumption from the viewpoints of both signal processing of a trigger signal and erroneous reception of a trigger signal from another company's vehicle.
The present invention has been made in view of such circumstances, and an object thereof is to provide a tire air pressure monitoring system with reduced power consumption.

Hereinafter, means for achieving the above-described object and its operation and effects will be described.
The invention according to claim 1 is attached to each tire and transmits a signal signal including tire pressure information. The sensor unit receives the information signal and the tire pressure information included in the information signal. And a receiver that issues a warning relating to a decrease in tire air pressure based on the transmission of a trigger signal including request information that specifies the number of transmissions or the transmission time of the information signal to the sensor unit When the trigger signal is received, the gist of the sensor unit is to transmit the information signal for the number of transmissions or the transmission time specified in the request information included in the trigger signal.

  According to this configuration, when receiving the trigger signal, the sensor unit transmits the information signal for the number of transmissions or the transmission time specified in the request information included in the trigger signal, and then ends the transmission of the information signal. For this reason, even if the sensor unit of the own vehicle receives a trigger signal from another vehicle unintentionally, the information signal is not continuously transmitted. Therefore, it is possible to reduce the power consumption required for transmitting the information signal in the sensor unit.

  In addition, the number of transmissions or transmission time of the information signal is specified by the trigger signal. For example, by specifying a transmission time for transmitting a plurality of information signals or transmitting a plurality of information signals, it is possible to reduce the number of times a trigger signal is received by the sensor unit, and thus the number of signal processing. Thereby, the power consumption concerning the signal processing in a sensor unit can be reduced.

  According to a second aspect of the present invention, in the tire air pressure monitoring system according to the first aspect, the trigger device receives from the sensor unit the last information signal in the number of transmissions or transmission time specified in the request information. The gist of the present invention is to transmit a new trigger signal before the time predicted to be transmitted.

  According to this configuration, the trigger signal is transmitted before the last information signal at the designated number of transmissions or transmission time is transmitted from the sensor unit. Therefore, the sensor unit can receive a new trigger signal before the transmission of the information signal corresponding to the request information of the trigger signal is completed. Therefore, information signals can be transmitted continuously.

  According to a third aspect of the present invention, in the tire pressure monitoring system according to the second aspect, the sensor unit receives the new trigger signal before completing the transmission of the information signal according to the request information. Then, the gist is to start transmission of the information signal according to the request information included in the new trigger signal.

  According to this configuration, when a new trigger signal is received while the information signal corresponding to the request information of the trigger signal is transmitted in the sensor unit, the trigger signal is given priority. That is, transmission of the information signal corresponding to the request information of the prioritized trigger signal is started.

  According to a fourth aspect of the present invention, in the tire pressure monitoring system according to any one of the first to third aspects, the trigger signal includes request information specifying a transmission cycle of the information signal, and the information signal The transmission cycle is set shorter as the vehicle speed becomes higher, and when the sensor unit receives the trigger signal, the sensor unit is also designated by the number of transmissions or the transmission time specified in the request information included in the trigger signal. The gist is to transmit the information signal in a transmission cycle.

  As the vehicle speed increases, the information signal reception rate at the receiver decreases. According to the above configuration, the transmission cycle is set shorter as the vehicle speed increases. Thereby, when the reception rate is low, the transmission cycle of the information signal is shortened. For this reason, even if the vehicle speed is high, it is suppressed that the warning is delayed because the information signal is not received over a long period of time.

  According to a fifth aspect of the present invention, in the tire air pressure monitoring system according to the fourth aspect, the trigger device has a reception rate of the information signal from the specific sensor unit in the receiver being a predetermined value or less. A request specifying a transmission cycle shorter than the transmission cycle of the current information signal in the specific sensor unit recognized based on the ID code corresponding to the specific sensor unit and the trigger signal transmitted in the past when it is determined And when the sensor unit determines that the ID code included in the trigger signal is a code corresponding to itself, the information corresponding to the request information of the trigger signal is transmitted. The gist is to transmit a signal.

  According to the configuration, when it is determined that the reception rate of the information signal from the specific sensor unit is equal to or less than a certain value, the trigger machine and the ID code corresponding to the specific sensor unit and the current in the specific sensor unit A trigger signal including request information specifying a transmission cycle shorter than the transmission cycle of the information signal is transmitted. When the sensor unit determines that the ID code included in the trigger signal is a code corresponding to itself, the sensor unit transmits an information signal in accordance with the transmission cycle specified in the signal. Therefore, the transmission cycle of the information signal in the sensor unit with a low reception rate can be shortened. Thereby, even when the reception rate of a specific sensor unit is poor, the information signal is not received from the sensor unit over a long period of time, and thus the delay of the low air pressure warning is suppressed.

  According to the present invention, power consumption can be reduced in a tire pressure monitoring system.

The block diagram of a tire pressure monitoring system. The timing chart which showed the vehicle speed, the trigger signal, and the information signal. (A) is the flowchart which showed the process sequence which concerns on transmission of the trigger signal St of CPU11 of the receiver 10, (b) is the flowchart which showed the process procedure which concerns on transmission of the information signal of CPU31 of sensor units 30a-30d.

Hereinafter, an embodiment of a tire pressure monitoring system (TPMS: Tire Pressure Monitoring System) embodying the present invention will be described with reference to FIGS.
As shown in FIG. 1, sensor units 30 a to 30 d are provided on the valve portions of the wheels W <b> 1 to W <b> 4 of the vehicle 1. Specifically, the sensor unit 30a is provided on the right front wheel W1, and the sensor unit 30b is provided on the left front wheel W2. The right rear wheel W3 is provided with a sensor unit 30c, and the left rear wheel W4 is provided with a sensor unit 30d.

(vehicle)
The receiver 10 mounted on the vehicle 1 includes a CPU 11, a receiving circuit 12, a receiving antenna 12 a, a memory 13, and a timer 18. An indicator 15, a trigger machine 16, and a vehicle speed sensor 17 are electrically connected to the CPU 11.

  The memory 13 stores threshold values used for low air pressure warnings and ID codes ID1 to ID4 corresponding to the sensor units 30a to 30d. These ID codes ID1 to ID4 are associated with wheel mounting positions.

  The receiving circuit 12 receives the information signal Si transmitted from each sensor unit 30a-30d via the receiving antenna 12a. Then, the receiving circuit 12 demodulates the received information signal Si and outputs the demodulated information signal Si to the CPU 11. The CPU 11 recognizes the ID codes ID1 to ID4 included in the demodulated information signal Si and tire pressure information.

  CPU11, after recognizing which wheel W1-W4 information is based on collation with ID code ID1-ID4 included in received information signal Si and ID code ID1-ID4 stored in memory 13, The tire pressure is recognized based on the pressure information included in the signal.

  When the tire pressure becomes equal to or less than the threshold value stored in the memory 13, the CPU 11 issues a warning that the air pressure is reduced for any of the wheels W <b> 1 to W <b> 4 through the indicator 15.

  Further, the CPU 11 generates a trigger signal St and outputs it to the trigger device 16. Here, the trigger signal St requests the sensor units 30a to 30d to transmit the information signal Si, and specifies the number of transmissions and the transmission cycle. Specifically, the trigger signal St includes ID information, transmission count information, and transmission cycle information. The trigger device 16 modulates the trigger signal St from the CPU 11 into a radio wave of UHF (Ultra High Frequency) band, and wirelessly transmits the signal.

  The CPU 11 determines that the vehicle is running when the vehicle speed is equal to or higher than a certain speed through the vehicle speed sensor 17. The CPU 11 transmits the trigger signal St at every predetermined period only while the vehicle is traveling. In this example, the vehicle speed is divided into a low speed region and a high speed region above a certain speed. In the low speed region, the CPU 11 includes the first cycle T1 as the transmission cycle information in the trigger signal St. Further, the CPU 11 includes a second cycle T2 shorter than the first cycle T1 in the trigger signal St as transmission cycle information in the high speed region.

  Further, the CPU 11 includes, in the trigger signal St, information requesting that the information signal Si be transmitted six times as the transmission count information in the low speed region. Further, the CPU 11 includes, in the trigger signal St, information requesting that the information signal Si be transmitted nine times as the transmission frequency information in the high-speed area. Further, the CPU 11 includes information indicating that the ID code is not normally specified as the ID information in the trigger signal St.

  The CPU 11 calculates the timing for transmitting the next trigger signal St when the trigger signal St is transmitted. Specifically, the CPU 11 calculates a certain time T3 by the product of a value obtained by subtracting, for example, “2” from the number of transmissions of the information signal Si included in the trigger signal St and the periods T1 and T2. As shown in FIG. 2, this fixed time T3 is the time from the transmission of the trigger signal St until the fifth information signal is transmitted in the low speed region, and from the transmission of the trigger signal St in the high speed region. It is the time before the eighth information signal is transmitted. In any case, the fixed time T3 elapses before the number of transmissions of the information signal Si reaches the number of times of transmission information.

  The CPU 11 measures the time through the timer 18 from the time when the trigger signal St is transmitted, and transmits the trigger signal St again when it is determined that the calculated fixed time T3 has elapsed. The retransmitted trigger signal St is also added with transmission frequency information and transmission cycle information according to the vehicle speed.

  As described above, the CPU 11 transmits the trigger signal St without waiting for reception for the number of transmissions of the transmission number information. For example, when the information signal Si is requested to be transmitted six times through the trigger signal St, the next trigger signal St is transmitted before the fifth information signal Si is received. When the CPU 11 determines that the information signal Si cannot be received in a cycle corresponding to the transmission cycle information included in the signal after transmitting the trigger signal St, the CPU 11 retransmits the trigger signal St. As a result, the trigger signal St is not received by the sensor units 30a to 30d, so that the transmission of the information signal Si is suppressed even though the vehicle speed is equal to or higher than a certain speed.

  When the information signal Si is not received from the specific sensor units 30a to 30d for a long time during traveling, the CPU 11 issues a warning that the specific sensor units 30a to 30d are abnormal through the indicator 15.

  The positions of the sensor units 30a to 30d change as the tire rotates. Depending on the positions of the sensor units 30a to 30d, the metallic wheel of the tire may become a radio wave obstacle. In this case, a null point is formed and the information signal Si is not received by the receiver 10.

  Further, depending on the distance between the sensor units 30a to 30d and the receiver 10, radio waves that are directed directly from the sensor units 30a to 30d to the receiver 10 and radio waves that are reflected from the sensor units 30a to 30d and reflected from the ground to the receiver 10 May interfere with each other, and the signal strength of the information signal Si in the receiver 10 may be significantly reduced. Also in this case, the information signal Si is not received by the receiver 10 as described above. Furthermore, when the vehicle speed increases, the possibility that the information signal Si is not received by the receiver 10 increases. As described above, the reception rate of the information signal Si in the receiver 10 may be lowered due to various factors. Hereinafter, processing when the reception rate is low will be described.

  The CPU 11 recognizes the reception rate based on the calculated fixed time T3 and the transmission count information included in the trigger signal St. For example, in a situation where the reception rate is 100%, four information signals Si are received within a certain time T3 in the low speed region. Therefore, the CPU 11 recognizes the reception rate as 50% when the information signal Si can be received only twice within the predetermined time T3.

  When the reception rate of the information signal Si from the specific sensor unit 30a to 30d is equal to or less than a certain value, the CPU 11 specifies the ID information specifying the ID codes ID1 to ID4 corresponding to the sensor unit 30a to 30d and the current information signal. A trigger signal St including transmission cycle information specifying a transmission cycle shorter than the transmission cycle of Si and transmission count information is transmitted. The number-of-transmissions information included in the trigger signal St at this time is determined according to the speed region as described above. Further, the current transmission cycle of the information signal Si is determined based on the transmission cycle information of the trigger signal St transmitted last time.

  When the reception rate is below a certain value, the warning is expected to be delayed to the extent that the user's convenience is hindered by the delay in receiving the information signal Si. Further, when the reception rate is below a certain value, the information signal Si is not received from the specific sensor units 30a to 30d for a long period of time, and a warning that there is an abnormality in the specific sensor unit is given. There is a fear. Such a situation can be solved early by retransmitting the trigger signal St.

(Sensor unit)
The sensor units 30a to 30d are, as shown in an enlarged view on the lower side of FIG. 1, a pressure sensor 33, a CPU (Central Processing Unit) 31, a transmission circuit 32, a transmission antenna 32a, a reception circuit 37, and a reception. An antenna 37a and a memory 35 are provided. Note that a battery (not shown) is built in each of the sensor units 30a to 30d, and the power of the battery is supplied to each of the above components.

In the nonvolatile memory 35, ID codes ID1 to ID4 unique to the sensor units 30a to 30d are stored.
The pressure sensor 33 detects the pressure of the tire and outputs the detection result to the CPU 31. The CPU 31 recognizes the tire pressure based on the detection result from the pressure sensor 33.

  The receiving circuit 37 receives the trigger signal St transmitted from the vehicle 1 via the receiving antenna 37a. Then, the reception circuit 37 demodulates the received trigger signal St and outputs the demodulated trigger signal St to the CPU 31. The CPU 31 recognizes the ID information, transmission count information, and transmission cycle information included in the trigger signal St.

  When the CPU 31 recognizes the ID information indicating that the ID code is not specified, the CPU 31 generates the information signal Si until the number of times included in the number-of-transmissions information is reached for each of the periods T1 and T2 included in the transmission cycle information. The data is output to the transmission circuit 32. The transmission circuit 32 modulates the information signal into a radio wave in the UHF band, and wirelessly transmits the signal via the transmission antenna 32a. That is, when the trigger signal St includes ID information indicating that the ID code is not specified, the information signals Si from all the sensor units 30a to 30d can be requested through the trigger signal St.

Here, the information signal is composed of a plurality of identical or single frames with ID codes ID1 to ID4 and pressure information as one frame.
When the CPU 31 receives a new trigger signal St before completing the generation and transmission of the information signal Si by the number of times included in the transmission frequency information, the CPU 31 gives priority to the new trigger signal St and the number of transmissions included in the signal. Generation and transmission of the information signal Si corresponding to the information and the transmission cycle information are started. Thereby, the transmission cycle of the information signal Si can be changed more quickly.

  Further, when the CPU 31 recognizes that the ID information of the received trigger signal St includes information indicating that any one of the ID codes ID1 to ID4 is included, the specified ID code ID1 to ID4, Collation with the ID codes ID1 to ID4 stored in the memory 35 is performed. That is, the ID code verification is established in any of the sensor units 30a to 30d. When the CPU 31 determines that the ID code verification of the received trigger signal St is established, the CPU 31 shortens the transmission cycle of the information signal Si based on the transmission cycle information of the same signal from the current cycles T1 and T2. Thereby, the frequency | count of transmission of the information signal Si in fixed time can be increased only about sensor unit 30a-30d with a low receiving rate.

  Therefore, the information signal Si is not received from the specific sensor units 30a to 30d over a long period of time, and the delay related to the low air pressure warning is suppressed. In addition, it is possible to suppress an erroneous determination that the sensor unit is abnormal because the information signal Si is not received over a long period of time.

On the other hand, the CPU 31 in the sensor unit whose reception rate is not low determines that the ID code verification is not established, and does not change the transmission cycle of the information signal Si.
Next, a processing procedure related to transmission of the trigger signal St of the CPU 11 of the receiver 10 will be described with reference to the flowchart of FIG. The flowchart starts when the vehicle speed becomes equal to or higher than a certain speed, that is, at the start of traveling.

  First, the trigger signal St is transmitted through the trigger device 16 (S101). Since this trigger signal St is immediately after the start of traveling, ID information indicating that the ID code is not designated, transmission number information corresponding to the low speed region, and transmission cycle information are added. Then, a predetermined time T3 is calculated based on the transmission count information and transmission cycle information included in the trigger signal St (S102). The vehicle waits for the fixed time T3 to elapse from the transmission of the trigger signal St through the timer 18 (NO in S103), and when it is determined that the fixed time T3 has passed (YES in S103), the vehicle speed becomes less than the fixed speed. Is determined, that is, whether or not traveling has been completed (S104). If it is determined that the vehicle continues to travel (NO in S104), the trigger signal St is transmitted again (S101). At this time, for example, if the vehicle speed is in the high speed region, the trigger signal St includes transmission number information and transmission cycle information corresponding to the region. On the other hand, when it is determined that traveling has ended (YES in S104), the process ends without causing the trigger signal St to be transmitted again.

  Next, a processing procedure related to transmission of information signals by the CPU 31 of the sensor units 30a to 30d will be described with reference to the flowchart of FIG. The flowchart starts when the trigger signal St is received.

  First, ID information, transmission count information, and transmission cycle information included in the trigger signal St are recognized (S201). Then, the information signal Si is transmitted at a predetermined cycle based on the various information (S202). This completes the process. When a new trigger signal St is received during the execution of the process of the flowchart, the process being executed is terminated and the process is newly started according to the flowchart.

As described above, according to the embodiment described above, the following effects can be obtained.
(1) Upon receiving the trigger signal St, the sensor units 30a to 30d transmit the information signal Si by the number of transmissions specified in the trigger signal St, and then end the transmission of the information signal Si. For this reason, even if it is a case where the sensor units 30a-30d of the own vehicle receive the trigger signal St from other vehicles unintentionally, the information signal Si is not continuously transmitted. Therefore, it is possible to reduce power consumption required for transmission of the information signal Si in the sensor units 30a to 30d.

  In addition, by specifying the number of transmissions of the information signal Si in the transmission number information included in the trigger signal St, the number of receptions of the trigger signal St in the sensor units 30a to 30d, and thus the number of signal processing can be reduced. Thereby, the power consumption concerning the signal processing in sensor unit 30a-30d can be reduced.

  (2) The trigger signal St is transmitted again before the last information signal Si in the designated number of transmissions is transmitted from the sensor units 30a to 30d. Therefore, the sensor units 30a to 30d can receive a new trigger signal St before the transmission of the information signal Si corresponding to the transmission frequency information and the transmission cycle information of the trigger signal St is completed. Therefore, the information signal Si can be continuously transmitted to the sensor units 30a to 30d.

  (3) In the sensor units 30a to 30d, when a new trigger signal St is received during transmission of the information signal Si corresponding to the transmission frequency information of the trigger signal St, the trigger signal St is prioritized. That is, the transmission of the information signal Si corresponding to the number of times of transmission of the prioritized trigger signal St is started. Thereby, the transmission cycle of the information signal Si can be changed more quickly.

  (4) Generally, the reception rate of the information signal Si in the receiver 10 decreases as the vehicle speed increases. In the above embodiment, the transmission cycle is set shorter than the current state when the vehicle speed becomes a speed in the high speed region. Therefore, the transmission cycle of the information signal Si can be shortened when the reception rate is low. By shortening the transmission cycle, the number of transmissions of the information signal Si in a certain time can be increased. For this reason, even if it is a case where a receiving rate becomes low because vehicle speed becomes high, it is suppressed that the information signal Si is not received by the receiver 10 over a long period of time. In addition, the low air pressure warning is delayed and the false warning that the sensor unit is abnormal is suppressed.

  (5) The trigger device 16 includes a trigger including ID information specifying an ID code corresponding to the specific sensor unit 30a to 30d when the reception rate of the information signal Si from the specific sensor unit 30a to 30d is equal to or less than a predetermined value. The signal St is transmitted. When the sensor units 30a to 30d determine that the ID code included in the trigger signal St is a code corresponding to the sensor unit 30a to 30d, the sensor units 30a to 30d transmit the information signal Si in a cycle shorter than the current transmission cycle based on the transmission cycle information of the signal. To do. Therefore, the transmission cycle of the information signal Si in the sensor units 30a to 30d having a low reception rate can be shortened. As a result, even if the reception rate of a specific sensor unit 30a to 30d is poor, the information signal Si is not received from the sensor unit 30a to 30d for a long period of time, and thus a low air pressure warning is delayed. In addition, an erroneous warning that an abnormality has occurred in the sensor unit is suppressed.

  (6) Unlike the above embodiment, when the trigger signal St is received, the transmission of the information signal Si is started at a constant period, and when the end signal indicating the end is received, the information signal Si There is a configuration in which transmission is terminated. In this configuration, when the trigger signal St is erroneously received from another vehicle, the transmission of the information signal Si at a constant cycle is continued. On the other hand, in the above embodiment, the transmission of the information signal Si is terminated after the information signal Si is transmitted the number of times included in the transmission frequency information of the trigger signal St. For this reason, it is suppressed that transmission of information signal Si is continued after a vehicle stops based on information signal Si from other vehicles. Thereby, consumption of the battery power of the sensor unit can be suppressed.

  (7) Further, unlike the above embodiment, only when the sensor units 30a to 30d are provided with acceleration sensors and it is determined that the vehicle is traveling based on the detection results of the sensors, the information is obtained at regular intervals. There are configurations for transmitting signals. In the above embodiment, since the acceleration sensor in this configuration can be omitted, the sensor units 30a to 30d can be configured more simply.

  (8) When the CPU 11 determines that the information signal Si cannot be received in the cycle T1 corresponding to the transmission cycle information included in the signal after transmitting the trigger signal St in the low speed region, for example, the CPU 11 re-generates the trigger signal St. Send. Thereby, since the trigger signal St is not received, it is suppressed that the transmission of the information signal Si is ended even during traveling.

In addition, the said embodiment can be implemented with the following forms which changed this suitably.
In the above embodiment, the transmission periods T1 and T2 of the information signal Si are determined based on whether the vehicle speed is in the low speed region or the high speed region. However, the vehicle speed region is not limited to the above two regions, and the speed region may be set more finely. In this case, the transmission cycle is further finely set according to the speed region. Thereby, it sets so that the transmission cycle of an information signal may become short as vehicle speed becomes high.

  -Transmission number information in the said embodiment may be transmission time information. In this case, the CPU 31 of the sensor unit transmits the information signal Si over the transmission time of the transmission time information. Further, the CPU 11 of the receiver 10 transmits the trigger signal St again before the transmission time of the transmission time information has elapsed.

  In the above embodiment, when the CPU 11 determines that the reception rate of the information signal Si from the specific sensor units 30a to 30d is equal to or less than a predetermined value, the CPU 11 assigns ID codes ID1 to ID4 corresponding to the sensor units 30a to 30d. You may transmit the trigger signal St containing only the designated ID information. That is, the transmission number information and the transmission cycle information may be omitted from the trigger signal St at this time. In this case, the CPU 31 of the sensor unit shortens the transmission cycle of the information signal Si from the current transmission cycle when the ID code verification in the ID information of the received trigger signal St is established.

  In the above embodiment, when the sensor unit receives a new trigger signal St before completing the transmission of the information signal Si by the number of times included in the transmission frequency information of the trigger signal St, the sensor unit gives priority to the new trigger signal St. Was. However, even when a new trigger signal St is received, after the transmission of the information signal Si is completed by the number of times included in the transmission count information of the previous trigger signal St, the information included in the new trigger signal St Based on this, the information signal Si may be transmitted.

  In the above embodiment, the trigger signal St is transmitted without waiting for reception of the information signal Si corresponding to the number of transmissions in the transmission number information. However, the trigger signal St may be transmitted after receiving the number of transmissions of the transmission number information.

  In the above embodiment, the trigger signal St always includes ID information. However, in the case of ID information not specifying an ID code, the ID information may be omitted. In this case, the signal length of the trigger signal St can be shortened.

  In the above embodiment, the number of transmissions information and the transmission cycle information are added to the information signal Si, but the transmission cycle information may be omitted. Further, baud rate information specifying a baud rate may be added. The baud rate is a value indicating how many times modulation / demodulation can be performed per second. The sensor units 30a to 30d transmit the information signal Si at a baud rate corresponding to the baud rate information included in the trigger signal St. The larger the baud rate value, the more information can be transferred within a certain time, so the signal length can be shortened. By shortening the signal length, it is possible to improve the possibility that signal transmission can be completed while a null point is not formed between the sensor unit and the receiver. Thereby, the reception rate of the information signal Si can be improved.

  -In above-mentioned embodiment, although ID code ID1-ID4 was linked | related with the attachment position of the wheel, you may abbreviate | omit this correlation. Even in this case, a low air pressure warning is possible.

  In the above embodiment, the single trigger device 16 transmits the trigger signal St to all the sensor units 30a to 30d at the same time. However, the trigger machine 16 may be provided corresponding to each sensor unit 30a-30d. In this case, the CPU 11 transmits the trigger signal St including the ID information in which the ID code is designated through the trigger device 16 only to the sensor units 30a to 30d corresponding to the ID code. Further, this ID information may be omitted. In this case, it is necessary to shift the transmission timing of the trigger signal St from each trigger device 16. Thus, the CPU 11 can recognize which sensor unit 30a to 30d is the information signal Si based on the reception timing of the information signal Si.

  In the above embodiment, when the reception rate of the information signal Si from the specific sensor units 30a to 30d is equal to or less than a predetermined value, the transmission cycle of the information signal Si from the specific sensor units 30a to 30d is shortened through the trigger signal St. However, this series of processing may be omitted.

  In the above embodiment, the frequency band of the trigger signal St and the information signal Si is the UHF band, but it may be an LF (Low Frequency) band.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 10 ... Receiver, 16 ... Trigger machine, 30a-30d ... Sensor unit, 33 ... Pressure sensor.

Claims (5)

A sensor unit that is mounted on each tire and transmits an information signal including tire pressure information, and a warning regarding a decrease in tire air pressure based on the tire pressure information included in the information signal while receiving the information signal A tire pressure monitoring system comprising:
A trigger machine that transmits a trigger signal including request information designating the number of transmissions or transmission time of the information signal to the sensor unit,
When the sensor unit receives the trigger signal, the sensor unit transmits the information signal for the number of transmissions or the transmission time specified in the request information included in the trigger signal. In the tire pressure monitoring system according to claim 1,
The trigger machine transmits the new trigger signal before the time when the last information signal at the number of transmissions or the transmission time specified in the request information is predicted to be transmitted from the sensor unit. Monitoring system. In the tire pressure monitoring system according to claim 2,
When the sensor unit receives the new trigger signal before completing the transmission of the information signal according to the request information, the sensor unit transmits the information signal according to the request information included in the new trigger signal. Tire pressure monitoring system that starts transmission. In the tire pressure monitoring system according to any one of claims 1 to 3,
The trigger signal includes request information specifying a transmission cycle of the information signal,
The transmission cycle of the information signal is set shorter as the vehicle speed increases,
When the sensor unit receives the trigger signal, the tire pressure monitoring system transmits the information signal in the same designated transmission cycle for the number of transmissions or the transmission time specified in the request information included in the trigger signal. . In the tire pressure monitoring system according to claim 4,
When it is determined that the reception rate of the information signal from the specific sensor unit in the receiver is equal to or less than a predetermined value, the trigger device has transmitted an ID code corresponding to the specific sensor unit in the past Request information specifying a transmission cycle shorter than the transmission cycle of the current information signal in the specific sensor unit recognized based on the trigger signal, and transmitting the trigger signal.
When the sensor unit determines that the ID code included in the trigger signal is a code corresponding to the sensor unit, the sensor unit transmits the information signal according to the request information of the trigger signal.

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