KR20020062981A - Tyre condition monitoring system - Google Patents

Abstract

Particularly suitable monitoring systems for monitoring vehicle tire conditions (eg pressure or temperature) include passive sensors 102 and 104, an antenna 106 associated with the passive sensor, and a connection between the passive sensor and the antenna. Switching means 108. In the first state of the switching means, the antenna cannot transmit a signal generated by the passive sensor. In the second state of the switching means, the antenna may transmit a signal generated by the passive sensor. This switching means operates remotely using control signals. The control signal may be derived from the sum or difference of the high frequency signals F1 and F2 supplied to the filter 112. In an alternative embodiment, the control signal is the modulation frequency of an AM or FM modulated high frequency signal with a digital code.

Description

Tire condition monitoring system {TYRE CONDITION MONITORING SYSTEM}

By using wireless communication technology, it is possible to monitor tire characteristics such as temperature and pressure during tire use. In general, sensor devices include one or more surface acoustic wave ('SAW') devices as data transmission devices. The SAW device may be a SAW resonator that provides an indication of tire temperature and tire pressure in response to a question by the remote device about the SAW resonator.

The use of a SAW device as a tire embedded element in a wireless communication system is particularly desirable because the SAW device does not require extra power to function as a wireless transceiver. The SAW device acts as a radio transceiver by stimulating the SAW device with the generation of radio frequency energy and then receiving the radio frequency response transmitted by the SAW device in response to such stimulation. Thus, SAW devices are considered completely "passive" devices in that the output signals from these devices are generated in response to the input signals they receive without the need for separate power. If the sensors used in the tire to detect temperature, pressure, etc. do not require power, the built-in tire monitor does not need a built-in power supply. Such monitors can be used permanently to monitor the proper conditions of the tire.

A particularly preferred embodiment of the invention uses a SAW resonator that can act as both a tire condition sensor and a wireless communication device. It is true that such embodiments are particularly preferred, but the invention is not limited to such embodiments, and other embodiments may be applied to all manual in-tyre condition monitor devices.

The passive monitor devices known so far using SAW devices have a drawback that they can only be used if a limited number of distinctive features can be identified. The SAW device is made to have a characteristic frequency range, so for two tires adjacent to each other on a single axis, a SAW device with a characteristic frequency range is used in one tire and another feature for another tire. It was possible to distinguish tires by using SAW devices with a frequency range of. However, the use of a number of different characteristic frequency ranges has serious practical limitations on the number available, and therefore the number of tires that can be placed within the area of use of the interrogator without disturbing the various results caused by the interrogation. There is a limit.

The limited number of frequency ranges that can be used is partly due to technical problems, and partly due to radio frequency limitations that can be used without permission. For example, in many countries, the radio frequency that can be freely used without permission is the Industrial Scientific Medical (ISM) frequency, which is independent of the water level license of 868 MHz or 2.45 GHz. However, for practical manufacturing reasons, only frequencies in the 868 MHz band can be used practically. Thus, at this time, frequencies in the 2.45 GHz band are known to be too high for use with SAW devices. This is because the electrode inter-digital pitch associated with SAW devices for use in the 2.45 GHz band is too fine to produce with current manufacturing techniques.

Although SAW devices can be satisfactorily queried using 868 MHz band radio waves, the bandwidth available is only 2 MHz. Current manufacturing techniques allow SAW devices to be provided with an accurate frequency tolerance of ± 0.1MHz. However, under normal operating conditions, the SAW device will experience oscillation of the characteristic resonant frequency in the frequency band up to 0.5 MHz, so that even if SAW devices with different characteristic resonant frequencies are separated and questioned, The bandwidth available, irrespective of permission, will only be sufficient to answer each question for two or three sensors. If four or more SAW devices are provided within a conventional sensor network within a range of interrogation devices, the query of at least one SAW device will raise one response from the two devices, resulting in an ambiguous determination of the parameters being monitored. Will be.

The present invention is directed to a tire condition monitor device, wherein the tire component comprises means for controlling tire condition data transmission. The tire condition monitoring apparatus of the present invention may also include means for identifying the tire to which the present invention is connected to a remote interrogation device.

1 is a schematic circuit diagram of a first embodiment of the present invention.

2 is a schematic circuit diagram of a second embodiment of the present invention;

3 is a schematic circuit diagram of a third embodiment of the present invention;

4 schematically illustrates a tire condition monitoring apparatus according to an embodiment of the present invention.

5 shows a sequence for a question signal and an answer signal from a SAW device sensor.

FIG. 6 illustrates how the answer signal from the SAW device can be switched to provide specific real code digital encryption. FIG.

7 is a schematic illustration of a passive impedance / frequency conversion device centered on a SAW device.

FIG. 8 illustrates an extended sensor arrangement that can be used in a tire to measure parameters including pressure and temperature, speed and speed, tire identification, multi axis tension with wear, and the like.

It is an object of the present invention to assign individual features, not unique operating frequencies, to each of a plurality of sensors, so that each of the sensors can be distinguished from each other.

This first aspect of the invention includes a passive sensor, an antenna connected to the passive sensor, switching means for controlling the connection between the passive sensor antennas, and remotely operable control means for controlling the state of the switching means. Permitting the antenna to transmit a signal generated by the passive sensor in a first state of the switching means and allowing the antenna to transmit a signal generated by the passive sensor in a second state of the switching means It is to provide a device that can be.

Thus, in the device according to the invention, the operation of the passive sensor can only generate a receivable signal when the switching means is brought to said second state. Accordingly, the receiving sensor can be effectively switched to "on" or "off" as needed by the user. In this way, the signals received from the passive sensor are limited to the signals from the sensors to be queried at any time. This eliminates the measurement of errors on the parameters.

Preferably, said switching means are controlled by an encrypted radio frequency control signal. The control signal is coded so that only sensors with the corresponding encryption (code) can be "on" by the encrypted signal.

In the area of the first embodiment of the present invention, the encryption (or encoding) is provided by sending two radio signals to the sensor and applying the sum and difference of these signals to a filter having a characteristic pass frequency.

If the sum of the two radio signal frequencies (and in some cases the frequency difference) corresponds to the pass frequency of the filter, one gate signal will be generated to change the switching means to the second state. The wireless signal may be in the 2.45 GHz band. The pass filter may have a pass frequency between 30 MHz and 100 MHz and a pass bandwidth of only 1 MHz.

In the second embodiment area of the present invention, the encryption is provided by amplitude modulation or frequency modulation of the radio control signal. In this case, the radio control signal is sent to a detector circuit, which is connected to a filter having a pass frequency characterized by the output of the detector circuit. When the output of the detector circuit corresponds to the pass frequency of the filter, one gate signal is generated to change the switch means to the second state. The filter may have a pass frequency between 100 kHz and 10 MHz and a bandwidth of 0.5 MHz.

In a third embodiment area of the invention, the encryption is provided by a digitally encrypted radio signal sent to a digital filter. If the code of the radio signal matches the code of the digital filter, one gate signal will be generated to change the switching means to the second state.

The switching means preferably comprise means for generating a constant voltage in response to receiving a switching signal. The voltage invention means can be supplied to power by the switch signal itself. The voltage generating means may be a battery.

The switching means may be a field effect transistor or an amplifier.

The passive sensor may be composed of a SAW device and may be composed of one or more acoustic sensors. When the passive sensor is an acoustic sensor, an amplifier is preferably provided to enable amplification of the output from the sensor.

It is also desirable to provide a means for increasing the efficiency of the antenna connected to the acoustic sensor. A variable capacitor may be used as a means for increasing the efficiency of the antenna.

A second feature of the invention is to provide a method for querying a passive sensor via an antenna associated with the passive sensor, the method generating a predetermined switching signal and applying the switching signal as a switching means to the passive sensor. And controlling the connection between the antenna and the antenna.

According to the third embodiment of the present invention described above, the tire condition monitoring device comprises one or more sensors for detecting the condition of the tire, storage means for storing an identification code associated with the sensor, a signal from a remote querying device. Receiving means for receiving a signal, wherein the signal comprises a portion representing an identification code, comparing means for comparing the identification code received by the receiving means with an identification code stored in the storage means, of the received signal A switch for connecting the sensor to the receiving means in response to an indication (or indication) from the comparing means that the identification code matches the identification code stored in the storage means, and a power source for supplying power to the apparatus. .

The power supply can include means for generating electrical energy in the tire when the tire is in use and means for storing the electrical energy generated as above. Alternatively or additionally, it may include means for holding radio frequency energy received from outside the tire.

In one preferred embodiment of the invention, the means for generating electrical energy generates a predetermined number of pulses of electrical energy, such as a predetermined electrical energy of one pulse per revolution of the tire. In such a case, the device according to the invention may comprise a counter for storing the count of the number of revolutions of the tire. Advantageously, the interrogator may query the stored coefficients to determine the number of turns the tire has performed. This action may be particularly desirable for large tires such as those used in civil engineering. Such tires are often sent to the factory for cleaning. It is particularly important that the trimming treatment is carried out before the tire is over worn. By providing an indication of the total tire speed remotely, this speed can be used as the basis for determining when the tire should be investigated and no longer need servicing.

In one embodiment of the present invention, a piezoelectric device such as a PVDF device inserted into the tire structure may be used as a device for generating a pulse of electrical energy. For such a device, an electrical energy pulse will be generated as the tire is twisted when the tire portion into which the device is inserted comes in contact with the ground. The pulse will increase the counter number and charge the electrical storage device.

In another embodiment of the present invention, radio frequency energy is used to power tire embedded components that require power. The radio frequency energy can be conveniently derived from the radio frequency signal used to query the tire sensor. Some of this energy can be rectified to generate a DC current to power tire embedded components. If necessary, electrical storage devices are used to accumulate electrical energy derived from radio frequency signals.

Preferably, the electrical storage device uses a condenser as a means for storing the electrical energy. The power requirements of the system are very small, and by using a condenser rather than a secondary battery, the system can have a very long life and is undesirably unaffected by the harsh environment in which the system must operate.

Preferably the sensor is a sensor of SAW device use. However, as described above, the present invention is not limited to the SAW device using system and can be applied to all manual monitor systems. In particular, the present invention includes a system using a passive impedance / frequency conversion device.

In order for the device to operate, the received signal must include an element corresponding to an identification code stored in the storage device. If desired, the interrogator device can be pre-programmed to have an identification code for every tire (eg four wheel mode of a four wheeled vehicle) to be used together. Depending on the selection, the interrogator may sequentially generate interrogation signals corresponding to all possible ID codes for the tire type. For example, if an 8-bit binary identification code is used, there may be 256 different codes that may be associated with individual tires. The interrogator can generate all possible 256 identification codes in order, and after each code, the response is heard. You will receive a response corresponding to four different individual identification codes (for four-wheeled vehicles). The interrogator may then remember the question codes associated with the four tires to buy and then generate only those codes, or continue to generate all possible identification codes in the questioning process.

If it is deemed desirable to have a greater number of identification codes than can be ordered by the interrogator, the identification code of the individual tires is determined when the tire is mounted on the vehicle so that the interrogator can be determined. It would be necessary to provide a means to be programmed with such an identification code. This may be done, for example, by setting a coded signal that will cause a tire to generate a signal representing its identification code. In such a device, an identification code will be determined at a sufficient distance from other tires and it will be necessary to position the tire and the interrogator so that the identification signal does not trigger more than one tire to send its identification code. This is only possible when the tire is separated from the motor vehicle or when there is only one tire at each end of each axis of the motor vehicle. In such a case, the interrogator associated with each tire would have a sufficiently short range and would not generate a response from another tire.

According to another feature of the invention, the tire condition monitoring device comprises one or more sensors for detecting the condition of the tire, storage means for storing an identification code associated with the sensor, reception for receiving a signal from a remote interrogation device. Means, means for transmitting to a querying device signal indicative of a state that the sensor is to sense, means for sending a signal representing the identification code to the querying device, and a power source for supplying power to the device.

The power supply includes means for generating electrical energy in the tire when the tire is used. Additionally or alternatively, it may comprise means for holding radio frequency energy received from the outside of the tire, and may comprise means for storing the electrical energy.

The first and second features of the present invention merely provide each tire with an indication of the tire status detected by the detector in response to a question signal corresponding to a particular tire, but as a part of the question order also includes its own identification code. It can also be combined with the results to be generated. In general, the device operates by sending a signal that includes a portion corresponding to the identification code of the device. Such a device will then send the necessary signal indicating the detected condition and then a signal indicating the tire identification code. The sensor information is associated with the correct identification code by a combination of transmitting sensor information in response to the received signal as long as it includes a portion corresponding to the stored identification code, and transmitting the stored identification code to the end of the sensor information transmission sequence. High reliability is given to the interrogation device.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

A first embodiment 100 of the invention is shown in the circuit diagram of FIG. The first embodiment 100 includes two SAW elements 102 and 104 connected in parallel with each other. As is well known in the art, each SAW element 102, 104 is provided with a pair of interleaved electrodes deposited on a piezoelectric substrate. One electrode of each SAW element 102, 104 is connected to ground, and the other electrode of each element 102, 104 is connected to the common antenna 106 via a channel of the FET 108. This arrangement is controlled in the channel of the FET 108 by the current flow between the SAW elements 102 and 104 and the antenna 106 supplying a voltage to the gate of the FET 108. Thus, FET 108 may be referred to by its generic name, variable high frequency coupling element. In an alternative embodiment of the invention (not shown), the variable high frequency coupling element may be provided in the form of a pin diode rather than a FET. Also in alternative embodiments, two SAW elements (more or less) may be connected to the common antenna using variable high frequency coupling elements.

The voltage at the gate of the FET 108 is supplied by the virtual battery 110 in accordance with the high frequency input signal. Virtual batteries have not been used in the past in connection with passive sensors, but their operation has been known for many years and will be readily understood by those of ordinary skill in the art. The high frequency input signal for the virtual battery 110 is determined by the filter 112. In the first embodiment 100 shown in FIG. 4, the filter 112 is set to pass a signal having a frequency within a 1 MHz bandwidth about a 100 MHz frequency. Thus, only signals supplied to the filter 112, having a frequency of 99.5-100.5 MHz, may enter and exit the virtual battery 110. In view of the signal frequency supplied to the filter 112, the filter 112 may be fabricated using SAW elements.

The arrangement described in connection with FIG. 4 allows the SAW elements 102 and 104 to be switched on and off effectively as required by the user. By providing the FET 108 between the SAW elements 102 and 104 and their associated antennas 106, the SAW elements 102 and 104 through the antenna 106 are not supplied to the filter 112 with the appropriate frequency. Communication with) is restricted. In the first embodiment 100 of FIG. 1, when a signal having a frequency of 99.5-100.5 MHz is supplied to the filter 112, communication with the SAW elements 102, 104 may be made via the associated antenna 106. . This signal is passed through filter 112 to the virtual battery 110 and generates a voltage. The voltage from the virtual battery 110 is supplied to the gate of the FET 108 so that the required current flow between the SAW elements 102 and 104 and the antenna 106 for communication with the SAW elements 102 and 104 can be achieved. have. The SAW elements 102 and 104 are then considered to be switched "on" and can be queried in a conventional manner. SAW elements 102 and 104 may be configured to operate at frequency Fs in the 868 MHz band.

In the case where a plurality of individual passive sensors or passive sensor groups are each queried separately, FIG. 1 provides a means for separately switching the sensors or sensor groups from off conditions to on conditions when the sensors or sensor groups are queried. For example, the arrangement described above can be adopted. In the sensor network arranged in accordance with the invention, each individual sensor or filter associated with each sensor group is connected to a common signal mixer. The signal mixer is connected to the antenna to receive electromagnetic waves in the 2.45 GHz band. Thus, a signal for supplying a sensor associated with a sensor or a group of sensors may occur by transmitting two signals of different frequencies in the 2.45 GHz band for reception by the mixer antenna.

For example, the group of SAW elements 102 and 104 shown in FIG. 1 can be switched from the off condition to the on condition by transmitting a first frequency F1 of 2.5 GHz to a second frequency F2 of 2.4 GHz to the mixer antenna. . When received by the mixer antenna, the two frequencies F1 and F2 are mixed in the signal mixer. It is well known that mixing of two frequencies produces a sum (F1 + F2) and a difference (F1-F2) signals. Thus, signals having frequencies of 0.1 GHz (ie F1-F2) and 4.9 GHz (ie F1 + F2) are generated by the mixer and supplied to the filter 112 associated with the SAW elements 102 and 104. The filter 112 causes the 0.1 GHz signal to be supplied to the virtual battery 110 but blocks the 4.9 GHz signal. As described above, upon receiving a high frequency input signal, the virtual battery 110 supplies a voltage to the gate of the FET 108 to enable signal transfer between the SAW elements 102 and 104 and their associated antennas 106. do. The SAW elements 102 and 104 are thus effectively switched to an "on" condition and maintain this condition when the mixer antenna receives two command signals F1 and F2. The virtual battery uses the power of the input signal to generate a voltage. Energy loss occurs in the signal mixer and filter, but the 500mW power level allowed in the 2.45GHz band is sufficient to operate the virtual battery satisfactorily.

In a sensor network, each filter is set for a different frequency, even if the mixer is connected to a filter associated with a different sensor or group of sensors than previously (FIG. 1). As mentioned above, the filter frequency may have a 1 MHz bandwidth and may be centered on a frequency in the range of 30 to 100 MHz. Thus, by transmitting command signals having frequencies of 2.4 GHz and 2.5 GHz, the SAW elements 102 and 104 associated with the 100 MHz filter 112 are selectively switched on. The sum and difference signals of 0.1 GHz and 4.0 GHz are blocked by filters associated with other sensors in the sensor network. When different sensors or sensor groups are queried, different command signals F1, F2 are sent to generate the appropriate difference signals F1-F2. For example, when a sensor associated with a 50 MHz filter is queried, the difference signal required to switch the sensor to an "on" condition may be generated by sending a command signal having a frequency of 2.45 GHz and 2.5 GHz. Other sensors in the sensor network, including the SAW elements 102 and 104 associated with the 100 MHz filter 112, remain "on" or switch to an "off" condition. Thus wrong parameter measurements will be prevented.

The sensors to be queried can be quickly switched between "on" and "off" conditions, and the output signal generated by the sensor can be selectively processed by using synchronous sensing techniques.

A second embodiment 200 of the invention is shown in the circuit diagram of FIG. The second embodiment 200 incorporates a single SAW element 202 connected to the antenna 206 through the channel of the FET 208. The virtual battery 210 is connected to the gate of the FET 208, and the filter 212 is connected in series to the virtual battery 210. The arrangement of the aforementioned components of the second embodiment 200 is identical to the arrangement of the corresponding components of the first embodiment 100. However, the second embodiment 200 is the first embodiment in that a switching signal to be supplied to the virtual battery 210 through the filter 212 is generated using an amplitude modulated carrier command signal having a frequency fc of 2.45 GHz band. In the example 100 it was modified. The signal mixer of the first embodiment 100 is replaced in the second embodiment 200 by means 214 for generating a signal having a frequency based on the amplitude modulation frequency Fm of the carrier signal. The signal generating means 214 is shown in FIG. 2 as integrating a sensor diode 216 and a capacitor 218. The form and operation of the signal generating means 214 is apparent in the art. An antenna for receiving a command signal is connected to the signal generating means 214.

The sensor network can be arranged with a plurality of individual passive sensors or sensor groups which are connected to the signal generating means 214 via associated virtual batteries and filters. Referring to the first embodiment 100 of FIG. 1, each individual sensor or sensor group may be queried separately when each filter operates for a different frequency. In the second embodiment 200 of FIG. 2, the filter 212 associated with the individual SAW elements 202 operates on signals having a 1 MHz frequency. Therefore, when received by the antenna of the signal generating means 214, a command signal having 1 MHz amplitude modulation gives generation of a voltage by the virtual battery 210 and a 1 MHz signal generated by the means 214. do. As a result, the SAW element 202 is effectively switched to an "on" condition as discussed above. The SAW element 202 can then be queried in a conventional manner. Other sensors in the sensor network will still be held or switched off. Incorrect parameter measurements can thus be avoided.

The filter frequency is centered on a frequency ranging from 100kHz to 10MHz and can have a bandwidth of 0.5MHz. A sensor or group of sensors can be switched to an "on" condition by sending a command signal that is modulated appropriately at the operating frequency of the associated filter. With regard to the aforementioned filter frequency, the filter used in connection with the second embodiment preferably integrates separate inductor and capacitor components rather than SAW elements.

In addition to the existing modulation of the carrier signal, modulation can be achieved by repeatedly switching the carrier signal on and off.

The aforementioned first and second embodiments 100 and 200 incorporate individual SAW elements 202 or SAW element groups 102 and 104. However, passive sensors other than SAW elements may be used in the present invention. For example, an acoustic sensor or a group of acoustic sensors may be selectively queried using the present invention. Piezoelectric acoustic sensors (ie microphones) may be mounted to the surface, for example, and used to monitor crack propagation on the surface. One embodiment of the invention incorporating a piezoelectric acoustic sensor is similar to that described above. However, the voltage generated by the virtual battery associated with the acoustic sensor can be supplied to an amplifier for amplifying the output from the acoustic sensor. The output from the amplifier is grounded through a variable capacitor (ie VARICAP) or directed through the capacitor to the antenna. The antenna associated with the amplifier may be an antenna used for receiving the command signal. This arrangement can be set such that when supplying voltage from the virtual battery to the amplifier, the piezoelectric acoustic sensor is effectively switched to an "on" condition. When the acoustic sensor senses noise, the output from the sensor is amplified by the amplifier. Thus, the voltage at VARICAP (variable capacitor) increases. VARICAP's capacitance decreases as the stated voltage increases. This lowers the efficiency of the antenna associated with the acoustic sensor. Thus, when noise is detected by the acoustic sensor, a portion of the signal transmitted for reception by the sensor antenna is reflected. The degree of reflection depends on the amount of noise detected. Thus, the reflected signal can be sensed by itself to determine noise in the acoustic sensor. In this way, propagation of cracks (one example) can be monitored.

A third embodiment 300 of the present invention is shown in the circuit diagram of FIG. The third embodiment 300 is a second embodiment in which the virtual battery 210 generates a voltage to supply to the amplifier 302 of the piezoelectric acoustic sensor 304 and even a voltage to supply to the FET 208 of the SAW element 202. Embodiment 200 is a variation. As mentioned above, the output of amplifier 302 is supplied to ground via VARICAP 306 and to the antenna through capacitor 308. In a third embodiment 300, the antenna associated with the piezoelectric acoustic sensor is an antenna used to receive a command signal. When using the third embodiment 300, upon receiving a command signal with 1 MHz amplitude modulation, both the SAW element 202 and the piezoelectric acoustic sensor 304 are switched to an "on" condition. Thus, the arrangement is set so that the crack propagation can be monitored simultaneously with the strain measurement. When the acoustic sensor senses noise, the efficiency of the antenna receiving the modulation command signal is adversely affected and degraded, and part of the command signal is reflected. Nevertheless, the received command signal is strong enough for the virtual battery 210 to generate an adequate voltage to supply the amplifier 302 and the FET 208. The reflected signal can monitor crack propagation. In addition, the strain can be measured through the query of the SAW device 202 using the 868MHz band in the conventional manner.

In FIG. 4 a tire condition monitoring element 401 is shown. In use, the device will be mounted on a tire or tire surface. Although the present invention can be applied to various kinds of tires, it is particularly useful for large tires of the type used in civil installation machinery and large road vehicles.

This device includes one or more sensors 402. The sensors are based on SAW devices but may be in other passive forms. For example, the frequency conversion element may be a nanophase wire or strip, or other passive impedance, and may indicate tire pressure, tire temperature, and stress strain of the tire. However, the invention is not limited to these sensors and can operate as a sensor capable of generating signals different from pressure, temperature, and strain.

As is well known in the art, SAW device sensors can display the characteristics of the sensor in response to interrogation signals received from remote high frequency sources. The interrogation signal is received by an antenna 403 forming part of the element of FIG. 4, and when the switch 404 is closed, the antenna 403 and the sensor 402 can be used to remotely indicate the condition that the sensor senses. It works in a way.

The device of the present invention includes a storage and comparator element 405 capable of storing an identification code that identifies the device being queried, and furthermore, the tire to which the device is to be fixed. The formula code can take any conventional form, for example a 408 bit digital code form providing a total of 256 different code combinations.

Comparator / storage element 405 is powered from a power supply 406 that includes an energy storage element 407 and an electrical energy source 408. In the illustrated embodiment of the invention, the electrical energy source 408 is a piezoelectric element of PVDF material embodied in the tire wall. Such a device generates an electric pulse according to the distortion of the tire wall, so that when the tire rotates, one pulse of electric energy is generated per tire rotation. Pulses of electrical energy are transmitted to the electrical energy storage element 407 via the connection 409. The electrical energy storage element 407 may take any suitable form, but in a preferred embodiment is a form comprising a capacitor. In addition, the energy of the storage element may be powered by high frequency energy transmitted remotely.

The device of the present invention preferably also includes a counter 410 that increments or decrements by one count with each pulse of electrical energy generated by the piezoelectric element 408. Thus, the count maintained by the counter 410 may indicate the number of turns of the tire after the count is reset.

In use, the remote interrogation element sends a query signal to the monitoring element 401. The interrogation signal is received by the antenna 402. The interrogation signal includes a portion that carries an identification code. For example, the query signal may be a modulated high frequency signal having a portion that carries an identification code. The identification code carried by the modulated signal can be constructed using a suitable demodulator element. The switch 104 generally takes the open state, and if the identification code portion of the query signal does not correspond to the identification code stored in the storage device 405, the switch 404 will remain open and the sensor will not be queried. will be. Power for the demodulator and comparator is supplied from the energy storage device 407.

If the quality corresponds to a query code stored in the storage device 405 where the identification code portion of the signal corresponds, the switch 404 is closed and then the antenna 403 is connected to the sensor 402 in a conventional manner. As shown in FIG. 2, a burst of a query signal 411 of, for example, a 10 millisecond duration will generate a feature return signal 412. A series of interrogation signals 411 are scattered to provide the required duty cycle. After a predetermined number of query / return signal cycles, the switch 404 blocks the flow of the return signal to provide a digital signal corresponding to the identification code stored in the storage element 405. A schematic portion of this arrangement is shown in FIG. 6. First inquiry signal 411A generates characteristic return signal 412A to indicate digital output " 1. " The switch 404 is then opened so that the next query signal 311B does not generate a feature return signal. This provides a digital "0" response. The switch 104 closes again, and the next query signal 411C again generates a characteristic response 412C indicating digital " 1. "

The digital signal transmission arrangement repeats the identification code several times (preferred) to eliminate possible errors.

The signal indicative of the count maintained by the counter 410 may be sent as part of each query order, or only in accordance with a particular request identified by a particular digital coding of the query signal. In addition, proper operation of the switch 404 in combination with a burst of query signals may be used to digitally encrypt the count maintained by the counter 410.

The switch 404, the storage and comparator elements 405, the counter 410, and their associated control circuits can be conveniently formed of a single silicon element. The electrical storage element 407 may be comprised of a virtual battery that is part of a silicon element.

Like multiaxial strain sensors, silicon has a programmed number: That is, pure data from the sensor comparing the programmed number to produce a single output that can be more easily transmitted using the inventive arrangements, and a programmed number corresponding to an acceptable level of strain in each axis. Can have silicon.

The remote interrogation element issues a series of interrogation signals carrying different parts of the identification code. In this arrangement, the query element only receives a response when the issued query signal corresponds to an identification code carried by one of the elements in range of the query system. Alternatively, the interrogation system may be preprogrammed with identification codes of elements in range, and may issue only interrogation signals corresponding to specific elements.

If desired, the device can respond to the unique identification code as well as the master code. In this arrangement, by moving a particular tire and query element from the high frequency range of another tire, a master code can be transmitted and then induce transmission of an identification code associated with that particular tire. Using this, the stored tire can have an identification code identified just before engaging the tire to the vehicle, which can be programmed into the vehicle query element to query the particular tire while remaining in the vehicle.

An alternative embodiment of using an offset frequency to separate the various sensing elements is shown in FIG. 8. In the figure, each PIFC element has a fixed impedance element that provides an offset from its original resonance frequency. This effectively provides each PIFC with a unique beat frequency between the SAW modulated by the sensing element and the reference SAW. In this way, the high frequency interrogation signal will excite all devices simultaneously and numerous frequency pairs will be returned. Each pair of frequencies will consist of a reference SAW resonant frequency f1 and a modulated SAW frequency f2. Frequency f2 is f1 + (offset impedance + modulated impedance) * (impedance-frequency ratio).

Claims (18)

A passive sensor, an antenna associated with the passive sensor, switching means for controlling the connection between the passive sensor and the antenna, and remote operation control means for controlling the state of the switching means, In this case, the antenna cannot transmit the signal generated by the passive sensor in the first state of the switching means, and the antenna may transmit the signal generated by the passive sensor in the second state of the switching means. Device characterized in that. 2. An apparatus according to claim 1, wherein the switching means is controlled by a coded high frequency control signal. 3. The apparatus of claim 2, wherein the apparatus comprises a mixer for mixing two high frequency signals and a band pass filter connected to the output of the mixer, wherein the band pass filter corresponds to an output from the mixer corresponding to the pass frequency of the filter. Changing the switching means to the second state. 4. The apparatus of claim 3, wherein the high frequency signal is in the 2.45 GHz band. 3. The apparatus of claim 2, wherein the apparatus comprises a detector circuit for sensing a modulation frequency of a frequency modulated or amplitude modulated high frequency signal, and a band pass filter connected to the output of the detector, wherein the band pass filter is output from the detector. The switching means is changed to a second state when it corresponds to the pass frequency of the filter. 3. An apparatus according to claim 2, comprising a digital filter for changing the switching means to a second state when the digital code carried by the high frequency signal corresponds to the digital code of the digital filter. An apparatus according to any of the preceding claims, comprising means for generating a voltage upon receipt of a switching signal. 8. An apparatus according to claim 7, wherein the voltage generating means is powered by the switching signal itself. 8. An apparatus according to claim 7, wherein said voltage generating means comprises means for generating electrical energy in response to tire movement. 10. The device of claim 8 or 9, comprising a virtual battery. Apparatus according to any one of the preceding claims, wherein the switching means comprises a FET or an amplifier. A method of querying a passive sensor through an antenna associated with a passive sensor, the method comprising: 1) generating a designated switching signal, and 2) supplying the switching signal to a switching means to control the connection between the passive sensor and the antenna; Method comprising the above steps. As a tire condition monitoring element, One or more sensors for detecting tire conditions, Storage means for storing an identification code associated with the sensor, Receiving means for receiving from the remote query element a signal comprising a portion indicating an identification code, Comparison means for comparing the identification code received by the reception means with the identification code stored in the storage means, A switch for connecting the sensor to the receiving means according to the identification value from the comparator if the identification code of the received signal corresponds to the identification code stored in the storage means, and A power supply for supplying voltage to the device Tire condition monitoring device comprising a. 14. The tire condition monitoring device according to claim 13, wherein the power supply includes means for generating electrical energy in the tire as the tire is used, and means for storing the generated electrical energy. 14. The tire condition monitoring device according to claim 13, wherein said power supply means comprises means for capturing high frequency energy received from outside of the tire. Tire condition according to any of claims 13 to 15, characterized in that said means for generating electrical energy generates a specified number of electrical energy pulses, for example one electrical energy pulse per revolution of the tire. Supervisor element. A tire condition monitoring device, characterized in that the device for generating an electrical energy pulse is a piezoelectric device such as, for example, a PVDF device implemented in a tire structure. As a tire condition monitoring element, One or more sensors for detecting tire conditions, Storage means for storing an identification code associated with the sensor, Receiving means for receiving a signal from a remote query element, Means for transmitting a signal to the querying device indicating a condition detected by the sensor, Means for transmitting a signal indicative of the identification code to the querying element, and A power supply for supplying voltage to the device Tire condition monitoring device comprising a.