JP2012051499A - Tire sensor and tire condition monitoring device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a tire sensor that detects rotation of a tire, while suppressing increase of member count, and can change radio transmission frequency of a tire state according to rotation of the detected tire, and to provide a tire condition monitoring device using the tire sensor.SOLUTION: A sensor unit 3 as a tire sensor includes: a sensor unit controller 13 which measures a state of the tire which is attached to a wheel of a vehicle; and a transmitting circuit 14 which performs radio transmission of the data which shows a condition of the tire which the sensor unit controller 13 measured. The sensor unit 3 has a conductor in which either the sensor unit controller 13 or the transmitting circuit 14 is electrically insulated from the ground and the wheel, detects rotation of the wheel attached with the tire sensor based on an electrical condition of the conductor which varies according to change of distance of ground and semiconductor, and changes frequency of the radio transmission based on rotation of detected wheel.

Description

  The present invention relates to a tire sensor mounted on a vehicle wheel for measuring a tire condition, and a tire condition monitoring apparatus using the tire sensor.

  2. Description of the Related Art Conventionally, a wireless tire condition monitoring device has been used in order to check the condition of a tire mounted on a vehicle in a passenger compartment. Such a wireless tire condition monitoring device includes a tire sensor having a transmitter mounted on a wheel of each tire and a receiver mounted on a vehicle body of the vehicle. The tire sensor measures values such as tire pressure and tire temperature corresponding to the tire sensor, and wirelessly transmits data indicating the measured value from the transmitter. On the other hand, the receiver receives the data from the transmitter with an antenna and displays the state of each tire on a display provided in the driver's seat of the vehicle, for example.

  By the way, although it is necessary to grasp | ascertain the state of the tire mentioned above normally at the time of driving | running | working of the vehicle which the driver is driving the vehicle, it is not necessary to grasp | ascertain when the driver | operator who is not boarding the vehicle stops. Therefore, the transmitter of the monitoring device described above periodically transmits data indicating the state of the tire while the vehicle is running, but does not transmit the data while the vehicle is stopped.

  For example, a tire condition monitoring device described in Patent Literature 1 includes a tire sensor provided on a wheel of a wheel (tire), and a ground contact state detection unit provided on the tire. The contact state detection unit detects whether or not the tire is rotating based on whether or not the contact force from the ground acts on a predetermined part. When the ground contact force is detected by the ground contact state detection unit, the tire sensor transmits data indicating the tire state from the transmitter. Thereby, when the tire is not rotating, data indicating the tire state is not transmitted from the transmitter.

  As another tire condition monitoring device, as shown in FIG. 8, a tire sensor 50 provided on a tire wheel detects the rotation of the tire by an acceleration sensor 51. The tire sensor 50 is driven by electric power supplied from the primary battery 16. The sensor unit controller 13 transmits data indicating the measurement values measured by the pressure sensor 11 and the temperature sensor 12 from the transmission circuit 14 at a predetermined frequency based on the rotation of the tire detected by the acceleration sensor 51. Thereby, the data transmission frequency is adjusted according to the rotation state of the tire.

JP 2005-186749 A

  According to the transmitter in each tire condition monitoring device described above, the frequency of transmitting data can be changed according to the rotation of the tire. Therefore, it is possible to prevent data from being transmitted from the transmitter when the tire is not rotating.

However, in the apparatus described in Patent Document 1, since the ground contact state detection unit, which is a separate member from the transmitter, is added as a new constituent member, the number of members constituting the tire state monitoring device is naturally increased. Therefore, the trouble of installing the ground contact state detection unit on the tire is separately required. Similarly, in the other devices shown in FIG. 8, the number of members increases by the amount corresponding to the acceleration sensor. In addition, since the acceleration sensor is a sensor that is relatively vulnerable to impact, the accuracy of the measurement result is low, and the operation test of the acceleration sensor in a finished product takes time.

  The present invention has been made in view of such circumstances, and its purpose is to detect the rotation of the tire while suppressing the increase in the number of members, and to detect the tire condition according to the detected rotation of the tire. A tire sensor capable of changing the wireless transmission frequency of the tire and a tire condition monitoring device using the tire sensor are provided.

  In order to solve the above-mentioned problem, the invention according to claim 1 is a transmission unit that wirelessly transmits data indicating a state of a tire measured by the measurement unit and a measurement unit that measures a state of a tire mounted on a vehicle wheel. A tire sensor attached to the wheel, wherein one of the measurement unit and the transmission unit includes a ground and a conductor electrically insulated from the wheel, and the ground and the The rotation of the wheel on which the tire sensor is mounted is detected based on the electrical state of the conductor that changes according to the change in the distance to the conductor, and the frequency of the wireless transmission based on the detected rotation of the wheel The gist is to provide a control unit that changes

  According to such a configuration, one of the measurement unit and the transmission unit includes the conductor electrically insulated from the ground and the wheel, and the rotation of the wheel is detected based on the electrical state of the conductor. Therefore, the rotation of the wheel can be detected without providing a dedicated sensor for detecting the rotation of the wheel. As a result, even if the frequency of wireless transmission is changed, the tire sensor does not require a sensor to detect the rotation of the wheel. Sex will be maintained.

  Further, since the rotation of the wheel is detected using a conductor provided in advance in the tire sensor, the structure of the tire sensor is maintained in the same manner as in the prior art, and there is no further complexity. That is, the configuration for detecting the rotation of the wheel in the tire sensor can be simplified.

The invention according to claim 2 is the tire sensor according to claim 1, characterized in that the conductor is an antenna for wireless transmission included in the transmitter.
According to such a configuration, since rotation of the wheel is detected based on a change in an electrical state generated in the antenna, a dedicated sensor is not necessary for detection of wheel rotation. As a result, the tire sensor can suppress an increase in the number of parts and an increase in installation time, and can maintain reliability.

Further, by using an antenna that is a relatively large conductor in the tire sensor, it becomes possible to more accurately detect a change in the electrical state.
The invention according to claim 3 is the tire sensor according to claim 1, wherein a tire valve having a valve stem electrically insulated from the wheel is connected to the tire sensor, and the conductor is The gist is that the valve stem is electrically coupled to the measuring section.

  According to such a configuration, since the rotation of the wheel is detected based on a change in the electrical state generated in the valve stem constituting the measuring unit, a dedicated sensor is not necessary for detecting the rotation of the wheel. As a result, the tire sensor can suppress an increase in the number of parts and an increase in installation time, and can maintain reliability.

Further, by using a valve stem that is a relatively large conductor connected to the tire sensor, a change in the electrical state can be detected more accurately. In general, since the valve stem has an insulator (rubber) between the wheel stem and the wheel, insulation with the wheel is preferably maintained.

The invention according to claim 4 is the tire sensor according to any one of claims 1 to 3, wherein the change in the electrical state is a change in capacitance generated in the conductor. .
According to such a configuration, since the change in capacitance occurs based on the change in the distance between the conductor and the ground, the distance between the conductor and the ground changes due to the change in the capacitance. It is detected that the wheel is rotating. Thereby, a tire sensor can be set as a simple structure.

The invention according to claim 5 is the tire sensor according to any one of claims 1 to 3, wherein the change in the electrical state is a change in the induced voltage generated in the conductor.
According to such a configuration, the induced voltage changes based on the change in the distance between the conductor and the ground, and therefore the distance between the conductor and the ground changes as the induced voltage changes. That is, it is detected that the wheel is rotating. Thereby, a tire sensor can be set as a simple structure.

  The invention according to claim 6 is the tire sensor according to any one of claims 1 to 5, wherein the control unit reduces the frequency of the wireless transmission when rotation of the wheel is not detected. It is a summary.

  According to such a configuration, when the rotation of the wheel is not detected, the frequency of wireless transmission from the transmission unit is reduced, so that the power consumption of the tire sensor is reduced. Thereby, the lifetime of the power supply provided in the tire sensor can be extended.

  The invention according to claim 7 is the tire sensor according to any one of claims 1 to 6, wherein the control unit increases the frequency of the wireless transmission when the rotation of the wheel is detected. It is a summary.

  According to such a configuration, when the rotation of the wheel is detected, the frequency of wireless transmission from the transmission unit increases, so the tire state measured by the tire sensor is provided with higher frequency and accuracy, for example, to a monitoring device or the like Will be able to.

  In order to solve the above-described problem, an invention according to claim 8 is provided with a tire sensor that is provided in a tire of a vehicle, acquires the state of the tire, and wirelessly transmits data indicating the acquired tire state, and the vehicle A tire condition monitoring device provided with a receiving device that is provided on the vehicle body and receives the data transmitted by the tire sensor, wherein the tire sensor is the tire sensor according to any one of claims 1 to 7. The summary is that it consists of.

  According to such a configuration, data indicating the state of the tire can be transmitted according to the rotation of the wheel, so that the tire state monitoring accuracy is maintained at an appropriate level according to the rotation state of the wheel. Will be able to. That is, for example, unnecessary wireless communication can be suppressed. As a result, the tire sensor can suppress unnecessary wireless communication and extend the life of the power source, and the tire condition can also be suitably monitored as a tire condition monitoring device using the tire sensor. Since the period in which the data can be created is extended, the convenience is improved.

Therefore, according to the above-described invention, a tire that can detect the rotation of the tire and suppress the wireless transmission frequency of the tire state according to the detected rotation of the tire while suppressing an increase in the number of members. A sensor and a tire condition monitoring device using the tire sensor can be provided.

1 is a schematic configuration diagram showing a vehicle equipped with a tire condition monitoring device according to an embodiment of the present invention. Sectional drawing of the wheel and tire with which the sensor unit used for the tire condition monitoring apparatus of the embodiment was provided. The block diagram which shows the circuit structure of the sensor unit of the embodiment. The block diagram which shows schematic structure of the sensor unit controller of the embodiment. It is a schematic diagram explaining the electrostatic capacitance between the antenna of the sensor unit of the embodiment and the ground, (a) is a schematic diagram showing when the angle of the tire is 0 degrees, (b) is the angle of the tire Schematic diagram showing when the angle is 90 degrees, (c) is a schematic diagram showing when the tire angle is 180 degrees. It is a schematic diagram explaining the induced voltage between the antenna of the sensor unit of the embodiment and the ground, (a) is a schematic diagram showing when the angle of the tire is 0 degrees, (b) is the angle of the tire The schematic diagram which shows the time of 90 degree | times, (c) is the schematic diagram which shows when the angle of a tire is 180 degree | times. The block diagram which shows the circuit structure of the tire condition monitoring apparatus which concerns on other embodiment of this invention. The block diagram which shows the circuit structure of the conventional tire condition monitoring apparatus.

Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings.
FIG. 1 shows a vehicle 1 equipped with a tire condition monitoring device. The tire condition monitoring device includes four sensor units 3 as tire sensors that are respectively attached to four wheels 5 of the vehicle 1 and a receiver unit 4 as a receiving device installed on the vehicle body of the vehicle 1. The sensor unit 3 and the receiver unit 4 constitute a tire pressure monitoring device as a tire condition monitoring device.

  As shown in FIGS. 1 and 2, each sensor unit 3 is fixed to the wheel 5 on which the tire 6 is mounted so as to be disposed in the internal space of the tire 6. Each sensor unit 3 detects the state (internal air pressure, internal temperature, etc.) of the corresponding tire 6 and wirelessly transmits a signal including data indicating the detected tire state, that is, a tire state data signal.

  As shown in FIG. 2, the sensor unit 3 is integrally provided with a tire valve 3 a that penetrates the wheel 5. The tire valve 3a includes a cylindrical elastic member 3c that extends from the inside of the wheel 5 as an internal space of the tire 6 to the outside and extends outside, and a valve stem 3b that passes through the inside of the cylindrical elastic member 3c. have. The cylindrical elastic member 3c is an insulator made of a rubber member or a resin member having electrical insulation. The valve stem 3b is composed of a conductive metal member, and the inner end of the wheel 5 is connected to the sensor unit 3, while the outer side of the wheel 5 is different from the inner end of the wheel 5. An end portion projects from the cylindrical elastic member 3c, and a valve cap 3d is attached to the outer end portion. Thereby, the tire valve 3a is attached to the wheel 5 while maintaining high airtightness by being fitted to the wheel 5 by the cylindrical elastic member 3c penetrating the wheel 5.

As shown in FIG. 3, each sensor unit 3 includes a pressure sensor 11 constituting a measurement unit, a temperature sensor 12 constituting a measurement unit, a sensor unit controller 13 constituting a measurement unit and a control unit, and a transmission constituting a transmission unit. A circuit 14 and a transmission unit are provided, and an antenna 17 as a conductor is provided. Each sensor unit 3 operates with electric power supplied from a primary battery 16 that is a power source built in the sensor unit 3. The antenna 17 is electrically insulated from the ground E and the wheel 5.

  The pressure sensor 11 measures the internal air pressure of the corresponding tire 6 and outputs an electric signal Sp corresponding to the air pressure obtained by the measurement to the sensor unit controller 13. The temperature sensor 12 measures the internal temperature of the corresponding tire 6 and outputs an electric signal St corresponding to the temperature obtained by the measurement to the sensor unit controller 13. In this embodiment, since the antenna 17 is connected to the sensor unit controller 13, an electric signal Sa corresponding to the capacitance or voltage is input to the sensor unit controller 13 as the electrical state of the antenna 17. .

  The sensor unit controller 13 includes a microcomputer including a CPU, a RAM, and a ROM, and an ID code (identification code) that is unique identification information is registered in the ROM. This ID code is information used to identify the sensor unit 3 in the receiver unit 4 installed on the vehicle body.

  A transmission circuit 14 is connected to the sensor unit controller 13. The sensor unit controller 13 generates a tire condition data signal including air pressure data, temperature data, and an ID code, and outputs the tire condition data signal to the transmission circuit 14. The transmission circuit 14 is provided with a switching circuit 14A for switching connection / disconnection to the antenna 17. The switching circuit 14 </ b> A is switched to “connected” during wireless transmission to connect the antenna 17 to the transmission circuit 14, and is switched to “not connected” other than during transmission to make the antenna 17 high with respect to the sensor unit controller 13. Maintain impedance. The transmission circuit 14 modulates the tire condition data signal from the sensor unit controller 13 into an RF signal (high frequency signal) having a predetermined carrier frequency, switches the switching circuit 14A to “connection”, and transmits the RF signal to the antenna 17. To send wirelessly.

  As shown in FIG. 4, the sensor unit controller 13 includes a sensor interface 20, a rotation detection unit 21, and a transmission controller 22. The sensor interface 20 converts various electric signals including voltages and capacitances input from various sensors and measurement objects into data suitable for processing by the sensor unit controller 13 as necessary. It is. Since the sensor interface 20 is provided with a switcher 20A that selects an electric signal to be subjected to data conversion processing from various input electric signals, in the sensor interface 20, the electric signal selected by the switcher 20A is data. Converted. The switcher 20 </ b> A switches the connection destination sensor based on a signal from the sensor unit controller 13. Therefore, the sensor unit controller 13 switches and selects the sensor to which the switch 20A is connected, so that the required electrical signal of the sensor is input to the sensor interface 20. The sensor unit controller 13 switches the sensor to be connected based on a preset condition, for example, a condition relating to a fixed period, a fixed interval, the presence or absence of rotation of the wheel 5, and the like. In addition, the sensor interface 20 can reduce electrical influences on various sensors and measurement objects connected thereto, and can efficiently receive electrical signals from the sensors.

Since the sensor interface 20 receives the electrical signal Sp when the electrical signal Sp corresponding to the air pressure from the pressure sensor 11 is selected by the switch 20A, the air pressure data based on the received electrical signal Sp is obtained as necessary. Generate. The sensor interface 20 receives the electrical signal St when the electrical signal St corresponding to the temperature from the temperature sensor 12 is selected by the switcher 20A. Therefore, the temperature based on the received electrical signal St is obtained as necessary. Generate data. Furthermore, since the sensor interface 20 receives the electric signal Sa when the electric signal Sa corresponding to the capacitance from the antenna 17 is selected by the switch 20A, the sensor interface 20 receives the electric signal Sa as necessary. Capacitance data is generated by measuring the based capacitance. Alternatively, for example, the sensor interface 20 may generate induced voltage data by measuring a voltage based on the electrical signal Sa received from the antenna 17. Note that the switcher 20A selects the electric signal Sa from the antenna 17 when necessary, but the sensor interface 20 is supplied with electric power from the antenna 17 because transmission power is supplied to the antenna 17 during wireless transmission. The signal Sa is not converted into capacitance data. Of the data generated by the sensor interface 20, air pressure data and temperature data are input to the transmission controller 22, and capacitance data are input to the rotation detection unit 21.

  By the way, the electrostatic capacity of the antenna 17 is defined according to the installation state of the sensor unit controller 13 and the antenna 17 with respect to the wheel 5, and shows a predetermined change according to the movement of the wheel 5. Therefore, in the present embodiment, the sensor unit controller 13 and the antenna 17 are installed on the wheel 5 so that a change that can determine the rotation of the wheel 5 occurs in the capacitance data.

  Among the installation states of the sensor unit controller 13 and the antenna 17 on the wheel 5, the installation state in which suitable capacitance data can be acquired in the present embodiment is an experiment or simulation carried out in advance, It is determined by the installation.

  The rotation detection unit 21 performs a process of detecting the rotation of the tire 6 (wheel 5) based on the capacitance data, and thus the tire 6 (wheel) based on the capacitance data input from the sensor interface 20. 5) Rotation is detected. In the rotation detection unit 21, the rotation detection program stored in the ROM or the like of the sensor unit controller 13 is executed by the CPU of the sensor unit controller 13, whereby the rotation detection process of the tire 6 is performed. In the rotation detection process, it is detected whether or not the tire 6 is rotating based on, for example, comparing a change that occurs in the capacitance data with a preset rotation detection condition. When the tire 6 is rotating, the rotation detection unit 21 may further detect the rotation speed. Information on whether or not the tire 6 obtained as a result of the rotation detection process by the rotation detection unit 21 is rotating is input to the transmission controller 22.

  Note that the rotation detection condition in the present embodiment is set as follows. That is, for the sensor unit controller 13 and the antenna 17 mounted on the wheel 5, comparison data is generated as capacitance data for setting rotation detection conditions based on previous experiments and simulations and measurement of capacitance in an actual vehicle. Is done. Various conditions such as characteristic values and changes necessary for detecting the rotation of the wheel 5 are extracted from the comparison data, and the extracted conditions are set as the rotation detection conditions. Such a rotation detection condition may be one or a plurality of threshold values, map data, an arithmetic expression, or the like as long as the rotation of the wheel 5 can be detected.

The transmission controller 22 generates a tire condition data signal including air pressure data, temperature data, and an ID code to be output to the transmission circuit 14 and adjusts (controls) the frequency of wireless transmission of the tire condition data signal by the transmission circuit 14. . While the pneumatic pressure data and the temperature data are input to the sensor interface 20, the rotation detection processing result is input from the rotation detection unit 21. Thus, the transmission controller 22 generates a tire condition data signal including air pressure data and temperature data, and causes the transmission circuit 14 to perform wireless transmission based on the result of the rotation detection process. For example, when a result that the tire 6 is not rotating is obtained by the rotation detection process, the transmission controller 22 reduces the frequency of wireless transmission by preventing the transmission circuit 14 from wirelessly transmitting the tire state data signal. . On the other hand, when the result that the tire 6 is rotating is obtained by the rotation detection process, the transmission controller 22 increases the frequency of wireless transmission by causing the transmission circuit 14 to wirelessly transmit the tire condition data signal. . In this case, the tire condition data signal is periodically transmitted at a predetermined time interval, for example, every one minute interval. Thereby, when the tire 6 is not rotating and the monitoring of the tire condition is unnecessary, the transmission controller 22 suppresses the wireless transmission with a large amount of power consumption to suppress the consumption of the primary battery 16 and the life of the primary battery 16. Try to extend On the other hand, when the tire 6 is rotating and the tire condition needs to be monitored, the transmission controller 22 appropriately transmits the tire condition data signal wirelessly so that the tire condition monitoring device can suitably monitor the tire condition. To be done.

  As shown in FIG. 1, the receiver unit 4 is installed at a predetermined location of the vehicle body, and operates by power from a battery (not shown) of the vehicle 1, for example. The receiver unit 4 includes at least one antenna 32, a receiver unit controller 33, a receiving circuit 35, an alarm device 37, and a display 38. The receiver unit controller 33 includes a microcomputer including a CPU, a ROM, and a RAM.

  The receiving circuit 35 demodulates a signal (tire condition data signal) received from each sensor unit 3 through the antenna 32 and sends the demodulated signal to the receiver unit controller 33. The receiver unit controller 33 grasps the internal air pressure and the internal temperature of the tire 6 corresponding to the transmission source sensor unit 3 based on the tire condition data signal from the receiving circuit 35.

  The receiver unit controller 33 also causes the display 38 to display information relating to the internal air pressure and internal temperature of the tire 6. The indicator 38 is arranged in the visible range of the passenger of the vehicle 1 such as the passenger compartment. Further, the receiver unit controller 33 notifies an alarm (notifier) 37 of an abnormality in the internal air pressure and internal temperature of the tire 6. As the alarm device 37, for example, a device for notifying abnormality by sound or a device for notifying abnormality by light is applied. In addition, you may display the abnormality of internal air pressure and internal temperature on the indicator 38 as an alarm.

  Next, the rotation detection processing of the tire 6 (wheel 5) performed by the sensor unit 3 of the present embodiment will be described more specifically based on examples. In the first embodiment, a case where the rotation of the wheel 5 is detected based on the capacitance measured from the antenna 17 will be described. In the second embodiment, the case where the rotation of the wheel 5 is detected based on the voltage measured from the antenna 17 will be described for an example in which the voltage is measured from the antenna 17 instead of the capacitance.

Example 1
As shown in FIG. 3, since the sensor unit 3 and the antenna 17 are not grounded with respect to the ground E, they are electrically floating with respect to the so-called ground E. Therefore, the sensor unit 3 has a capacitance Co between the sensor unit 3 and the wheel 5 to which the sensor unit 3 is attached. The antenna 17 is maintained at a high impedance with respect to the sensor unit controller 13 (the sensor interface 20 and the transmission controller 22) when not wirelessly transmitting, and therefore differs from the capacitance Co of the sensor unit controller 13. It has a capacitance Ci between the ground E. Thereby, when the sensor unit controller 13 measures the capacitance of the antenna 17, the capacitance (Ci-Co) relative to the sensor unit controller 13 can be obtained as the capacitance of the antenna 17.

In general, the capacitance C is represented by the following formula (1) using the charge Q and the voltage Vt. Further, the voltage Vt is expressed by the following equation (2) using the electric field Ef and the interelectrode distance d. From this, it is obtained by the following formula (3) that the capacitance C changes so that its value is inversely proportional to the interelectrode distance d. On the other hand, since the relationship between the dielectric constant ε, the electrode area S, and the inter-electrode distance d is expressed by the following equation (4), the capacitance C has a value corresponding to the electrode It changes so as to be inversely proportional to the distance d.

C = Q / Vt (1)
Vt = Ef · d (2)
C = Q / (Ef · d) (3)
C = ε · S / d (4)
As shown in Expression (3) and Expression (4), the electrostatic capacity Ci of the antenna 17 varies depending on the inter-electrode distance d from the ground E. For this reason, it is possible to detect that a change has occurred in the distance between the antenna 17 and the ground E, that is, that the wheel 5 (tire 6) has been rotated based on the change in the capacitance Ci. The sensor unit 3 has a capacitance Co between the wheel 5 and the wheel 5, but the wheel 5 is electrically stable because the distance to the ground E is substantially constant or relatively large. The capacitance Co of the sensor unit 3 arranged at a distance close to 5 is substantially constant.

  FIG. 5 is a diagram schematically illustrating the distance between the sensor unit 3 and the ground E for each of the cases where the rotation angle of the wheel 5 is 0 degrees, 90 degrees, and 180 degrees. FIG. 5A is a diagram illustrating a case where the sensor unit 3 is the distance d1 closest to the ground E because the angle of the wheel 5 is 0 degrees. FIG. 5B is a diagram illustrating a case where the sensor unit 3 has a medium distance d2 to the ground because the angle of the wheel 5 is 90 degrees. FIG. 5C is a diagram illustrating a case where the sensor unit 3 is at a distance d3 farthest from the ground because the angle of the wheel 5 is 180 degrees.

  As shown in FIG. 5A, the sensor unit controller 13 has a capacitance Co, and when the angle of the wheel 5 is 0 degrees, the distance between the sensor unit 3 and the ground E is d1. The antenna 17 has a capacitance Ci1. Thereby, the sensor unit controller 13 obtains a relative capacitance (Ci1-Co) as the capacitance of the antenna 17. As shown in FIG. 5B, the sensor unit controller 13 has a capacitance Co, and when the angle of the wheel 5 is 90 degrees, the distance between the sensor unit 3 and the ground E is d2. Therefore, the antenna 17 has a capacitance Ci2. Thereby, the sensor unit controller 13 obtains a relative capacitance (Ci2-Co) as the capacitance of the antenna 17. Further, as shown in FIG. 5C, the sensor unit controller 13 has a capacitance Co, and when the angle of the wheel 5 is 180 degrees, the distance between the sensor unit 3 and the ground E is d3. Therefore, the antenna 17 has a capacitance Ci3. Thereby, the sensor unit controller 13 obtains a relative capacitance (Ci3-Co) as the capacitance of the antenna 17.

  For this reason, the rotation detection unit 21 of the sensor unit controller 13 changes the antenna 17 and the ground based on the change in the capacitance (relative capacitance) of the antenna 17 measured by the sensor unit controller 13. It can be detected that the distance to E is fluctuating, that is, that the wheel 5 (tire 6) is rotating.

  As described above, since the rotation of the wheel 5 is detected on the basis of a change in capacitance that is an electrical state generated in the antenna 17 provided in advance in the sensor unit 3, the rotation of the wheel 5 can be performed without providing another sensor. Can be detected.

(Example 2)
As shown in FIG. 3 and as described in the first embodiment, since the sensor unit 3 and the antenna 17 are not grounded with respect to the ground E, they are electrically floated with respect to the so-called ground E. Yes. The sensor unit 3 is surrounded by a magnetic field or an electric field based on natural noise or daily noise. Here, since the antenna 17 is maintained at a high impedance with respect to the sensor unit controller 13, the antenna 17 has an induced voltage Vi between the ground E and the influence of a magnetic field or an electric field surrounding the antenna 17. Thereby, when the sensor unit controller 13 measures the voltage of the antenna 17, the induced voltage Vi can be obtained as the voltage of the antenna 17 with respect to the sensor unit controller 13.

  In general, the voltage Vt is expressed by the above formula (2) by the electric field Ef and the interelectrode distance d. From this, the induced voltage of the sensor unit controller 13 and the antenna 17 changes due to the change of the inter-electrode distance d. On the other hand, since the relationship between the current i and the impedance (capacitance C) is expressed by the following formula (5), the voltage Vt is electrostatically affected by the interelectrode distance d as shown in the first embodiment. When the capacitance C changes, the voltage Vt changes according to the change in the capacitance C.

Vt = i · 1 / (jω · C) (5)
As shown in the equations (2) and (5), the induced voltage Vi of the antenna 17 varies depending on the inter-electrode distance d from the ground E. For this reason, it is possible to detect that a change has occurred in the distance between the antenna 17 and the ground E based on the change in the induced voltage Vi, that is, that the wheel 5 (tire 6) has rotated. Although the sensor unit 3 has a voltage Vo between the wheel 5 and the wheel 5, the wheel 5 is electrically stable because the distance to the ground E is substantially constant or relatively large. On the other hand, the voltage Vo of the sensor unit 3 arranged at a close distance is substantially constant.

  FIG. 6 is a diagram schematically illustrating the distance between the sensor unit 3 and the ground E for each of the cases where the rotation angle of the wheel 5 is 0 degrees, 90 degrees, and 180 degrees. FIG. 6A is a diagram illustrating a case where the sensor unit 3 is the distance d1 closest to the ground because the angle of the wheel 5 is 0 degrees. FIG. 6B is a diagram illustrating the case where the sensor unit 3 is at an intermediate distance d2 from the ground because the angle of the wheel 5 is 90 degrees. FIG. 6C is a diagram showing a case where the sensor unit 3 is at a distance d3 farthest from the ground because the angle of the wheel 5 is 180 degrees.

  As shown in FIG. 6A, when the angle of the wheel 5 is 0 degree, the distance between the sensor unit 3 and the ground E is d1, and therefore the antenna 17 has an induced voltage Vi1. Thereby, the sensor unit controller 13 obtains the induced voltage Vi <b> 1 as the voltage of the antenna 17. Further, as shown in FIG. 6B, when the angle of the wheel 5 is 90 degrees, the distance between the sensor unit 3 and the ground E is d2, and therefore the antenna 17 has an induced voltage Vi2. Thereby, the sensor unit controller 13 obtains the induced voltage Vi2 as the voltage of the antenna 17. Furthermore, as shown in FIG. 6C, when the angle of the wheel 5 is 180 degrees, the distance between the sensor unit 3 and the ground E is d3, and therefore the antenna 17 has an induced voltage Vi3. As a result, the sensor unit controller 13 obtains the induced voltage Vi3 as the voltage of the antenna 17.

  For this reason, in the rotation detection unit 21 of the sensor unit controller 13, the distance between the antenna 17 and the ground E is based on the change in the voltage (inductive voltage) of the antenna 17 measured by the sensor unit controller 13. Can be detected, that is, that the wheel 5 (tire 6) is rotating.

As shown in the present embodiment, since the rotation detection unit 21 of the sensor unit controller 13 detects the rotation of the wheel 5 (tire 6) based on the change in the capacitance or induced voltage of the antenna 17, the wheel 5 It is not necessary to install a dedicated sensor for detecting the rotation. In addition, the frequency of wireless transmission can be changed according to the rotation of the wheel 5. Furthermore, since the antenna 17 provided in advance in the sensor unit 3 is used, an increase in the number of parts as the sensor unit 3 and installation work are suppressed, reliability is maintained, and the structure is further complicated. There is no such thing. That is, the configuration for detecting the rotation of the wheel 5 in the sensor unit 3 can be simplified with a reduced number of members.

As described above, according to the tire valve unit of the present embodiment, the effects listed below can be obtained.
(1) The transmission circuit 14 includes an antenna 17 that is electrically insulated from the ground E and the wheel 5, and the rotation of the wheel 5 is detected based on the electrical state (capacitance and voltage) of the antenna 17. . Therefore, the rotation of the wheel 5 can be detected without providing a dedicated sensor for detecting the rotation of the wheel 5. Thus, even if the frequency of wireless transmission is changed, the sensor unit 3 does not require a sensor for detecting the rotation of the wheel 5, and the increase in the number of parts constituting the sensor unit 3 and the labor of installation can be suppressed. At the same time, reliability is maintained.

  (2) Since the rotation of the wheel 5 is detected using the antenna 17 provided in advance in the sensor unit 3, the structure of the sensor unit 3 is maintained in the same manner as in the prior art, and there is no further complexity. That is, the configuration for detecting the rotation of the wheel 5 in the sensor unit 3 can be simplified.

  (3) Since the rotation of the wheel 5 is detected based on a change in the electrical state generated in the antenna 17, a dedicated sensor is not required for detecting the rotation of the wheel 5. As a result, the sensor unit 3 is restrained from increasing the number of parts and the time and effort of installation, and the reliability can be maintained. In addition, by using the antenna 17 that is a relatively large conductor in the sensor unit 3, it is possible to more accurately detect a change in the electrical state.

  (4) Since the change in capacitance occurs based on the change in the inter-electrode distance d between the antenna 17 and the ground E, the distance between the antenna 17 and the ground E changes due to the change in capacitance. It is detected that the wheel 5 is rotating. As a result, the sensor unit 3 can have a simple configuration.

  (5) Since the change of the induced voltage is caused based on the change of the interelectrode distance d between the antenna 17 and the ground E, the distance between the antenna 17 and the ground E is changed by the change of the induced voltage. That is, it is detected that the wheel 5 is rotating. As a result, the sensor unit 3 can have a simple configuration.

  (6) Since the frequency of wireless transmission from the transmission circuit 14 is reduced when the rotation of the wheel 5 is not detected, the power consumption by the sensor unit 3 is reduced. Thereby, the lifetime of the primary battery 16 which is a power supply provided in the sensor unit 3 can be extended.

  (7) Since the frequency of wireless transmission from the transmission circuit 14 is increased when the rotation of the wheel 5 is detected, the tire pressure measured by the sensor unit 3 can be measured with higher accuracy, for example, via the receiver unit 4. The monitoring device can be acquired.

In addition, the said embodiment can also be implemented in the following aspects, for example.
In the above embodiment, the case where the antenna 17 is used as a conductor is illustrated. However, the present invention is not limited to this, and when an LF receiving circuit is provided in the sensor unit, the antenna of the LF receiving circuit may be used as a conductor. The LF receiving circuit is for receiving an LF signal as a command signal, and in response to receiving the LF signal transmitted from the external device having the LF transmitting circuit by the LF receiving circuit, the sensor The unit performs an operation according to the command content indicated by the LF signal. At this time, an LF transmission circuit may be provided in the receiver unit. Thereby, a freedom degree of design comes to be raised as a tire condition monitoring device.

  -In the above-mentioned embodiment, although illustrated about the case where valve stem 3b was constituted from a metal member which has conductivity, not only this but when an antenna is used as a conductor, valve stem is constituted from a hard member. If it is, it does not need to have electroconductivity. Thereby, the freedom degree of a structure of a sensor unit is raised.

  -In the said embodiment, when rotation of the wheel 5 is not detected, the frequency of radio transmission becomes low. Not limited to this, a configuration in which the frequency of previous wireless transmission is maintained may be maintained for a predetermined period after the rotation of the wheel 5 is not detected. Moreover, in the said embodiment, when rotation of the wheel 5 is detected, the frequency of radio transmission becomes high. Not only this but the structure where the frequency of the previous radio | wireless transmission is maintained for a predetermined period after the rotation of the wheel 5 is detected may be sufficient.

  -In above-mentioned embodiment, the case where the antenna 17 was used as a conductor which comprises a transmission part was illustrated. However, the present invention is not limited to this, and the conductor constituting the transmitter is insulated from the ground and the wheel, coupled (electrically coupled) to the sensor unit, and has a high impedance to the sensor unit controller. A metal member etc. may be sufficient. For example, as shown in FIG. 7, a valve stem 3b, which is a relatively large conductor connected to the sensor unit 3, may be used as a conductor. That is, the sensor unit 3 includes a valve stem 3b that is electrically insulated from the ground and the wheel, and the rotation of the wheel 5 is detected based on the electrical state of the valve stem 3b. Thereby, the sensor unit 3 can detect the rotation of the wheel based on the fluctuation of the electrostatic capacity Ci and the induced voltage Vi of the valve stem 3b measured from the electrically connected valve stem 3b. Become. Therefore, the rotation of the wheel 5 can be detected without providing a dedicated sensor for detecting the rotation of the wheel 5. As a result, the sensor unit can be further improved in design freedom and measurement accuracy.

  In addition, even if the frequency of wireless transmission is changed by this, the sensor unit 3 does not need a sensor for detecting the rotation of the wheel 5, and the number of parts constituting the sensor unit 3 and the labor of installation are increased. In addition to being suppressed, reliability is also maintained. Furthermore, since the rotation of the wheel 5 is detected using a valve stem 3b provided in advance in the sensor unit 3, the structure of the sensor unit 3 is maintained in the same manner as in the prior art, and there is no further complexity. That is, the configuration for detecting the rotation of the wheel 5 in the sensor unit 3 can be simplified.

  Further, since the rotation of the wheel 5 is detected based on a change in the electrical state generated in the valve stem 3b constituting the sensor unit 3, a dedicated sensor is not necessary for detecting the rotation of the wheel 5. As a result, the sensor unit 3 is restrained from increasing the number of parts and the time and effort of installation, and the reliability can be maintained.

  Furthermore, by using the valve stem 3b, which is a relatively large conductor connected to the sensor unit 3, it becomes possible to more accurately detect a change in the electrical state. In general, since the valve stem 3b has an insulator (rubber) between the valve stem 3b and the wheel 5, insulation with the wheel 5 is also preferably maintained.

  -The conductor is not limited to the antenna 17 of the above embodiment or the valve stem 3b of the above embodiment, and a conductor provided in the sensor unit and having a relatively large area can be adopted. . For example, a conductor provided for shielding electromagnetic waves or the like in a part of the sensor unit, a conductor provided as a lid for the case, or the like may be used. Thereby, the design freedom of such a sensor unit improves.

  In the above embodiment, the case where the sensor unit 3 is provided with the pressure sensor 11 and the temperature sensor 12 is illustrated. However, the present invention is not limited to this, and the sensor unit may be provided with a sensor other than the pressure sensor and the temperature sensor, for example, a sensor for measuring the tire condition. Thereby, the performance as a sensor unit comes to improve.

  In the above embodiment, the case where the primary battery 16 is provided in the sensor unit 3 is illustrated. However, the present invention is not limited thereto, and a secondary battery may be provided together with the primary battery, or a secondary battery may be provided instead of the primary battery. When a secondary battery is provided, a stable supply of drive power to the sensor unit can be achieved if a power generation device or the like for charging the secondary battery is provided.

  DESCRIPTION OF SYMBOLS 1 ... Vehicle, 3 ... Sensor unit, 3a ... Tire valve, 3b ... Valve stem, 3c ... Cylindrical elastic member, 3d ... Valve cap, 4 ... Receiver unit, 5 ... Wheel, 6 ... Tire, 11 ... Pressure sensor, DESCRIPTION OF SYMBOLS 12 ... Temperature sensor, 13 ... Sensor unit controller, 14 ... Transmission circuit, 16 ... Primary battery, 17 ... Antenna, 20 ... Sensor interface, 21 ... Rotation detection part, 22 ... Transmission controller, 32 ... Antenna, 33 ... Receiver unit Controller, 35 ... Receiver circuit, 37 ... Alarm, 38 ... Indicator, 50 ... Tire sensor, 51 ... Accelerometer, E ... Earth, Ci, Co ... Capacitance, Vi ... Induction voltage.

Claims (8)

A measurement unit that measures the state of the tire mounted on the wheel of the vehicle;
A transmission unit that wirelessly transmits data indicating the state of the tire measured by the measurement unit;
A tire sensor mounted on the wheel,
Either one of the measurement unit and the transmission unit has a conductor that is electrically insulated from the ground and the wheel,
Detecting the rotation of the wheel on which the tire sensor is mounted based on the electrical state of the conductor that changes according to the change in the distance between the ground and the conductor, and based on the detected rotation of the wheel A tire sensor comprising a control unit that changes the frequency of wireless transmission. The tire sensor according to claim 1, wherein the conductor is an antenna for wireless transmission included in the transmission unit. A tire valve having a valve stem electrically insulated from the wheel is connected to the tire sensor,
The tire sensor according to claim 1, wherein the conductor is the valve stem that is electrically coupled to the measurement unit. The tire sensor according to any one of claims 1 to 3, wherein the change in the electrical state is a change in capacitance generated in the conductor. The tire sensor according to any one of claims 1 to 3, wherein the change in the electrical state is a change in an induced voltage generated in the conductor. The controller is
The tire sensor according to any one of claims 1 to 5, wherein when the rotation of the wheel is not detected, the frequency of the wireless transmission is decreased. The controller is
The tire sensor according to any one of claims 1 to 6, wherein when the rotation of the wheel is detected, the frequency of the wireless transmission is increased. A tire sensor that is provided in a vehicle tire and wirelessly transmits data indicating the tire state acquired by acquiring the tire state; and the data that is provided in the vehicle body of the vehicle and transmitted by the tire sensor. A tire condition monitoring device comprising a receiving device for receiving,
The tire sensor comprises the tire sensor according to any one of claims 1 to 7. A tire condition monitoring device, characterized in that:

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