TIRE INFORMATION DETECTING SYSTEM

Abstract

A transponder includes an antenna, a modulation/demodulation unit (diode) that modulates and demodulates signals received and transmitted from and to a controller, a pressure resonator including a first piezoelectric single-crystal resonating element and a pressure sensor. The resonance frequency of the pressure resonator changes in accordance with a change in tire pressure, and a reference resonator includes a second piezoelectric single-crystal resonating element and a capacitor, where the resonance frequency of the reference resonator is unaffected by the change in tire pressure. The first and second piezoelectric single-crystal resonating elements are integrally formed on a single-crystal piece. The controller transmits a signal for resonating the pressure resonator and the reference resonator, receives signals modulated with the resonance frequencies of the pressure resonator and the reference resonator, and computes a measured value in accordance with the resonance frequencies of the two resonators retrieved from the received signals.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary circuit configuration of a transponder of a tire information detecting system according to an embodiment of the present invention;

FIG. 2 is a diagram illustrating the difference between the resonance frequency of a reference resonator and the resonance frequency of a pressure resonator in the transponder according to the embodiment of the present invention;

FIG. 3 is a diagram illustrating the difference between the resonance frequency of a reference resonator and the resonance frequency of a pressure resonator in the transponder according to the embodiment of the present invention;

FIG. 4 is a diagram illustrating a change in the difference between the resonance frequency of a reference resonator and the resonance frequency of a pressure resonator in the transponder according to the embodiment of the present invention;

FIG. 5 is a schematic illustration of a circuit diagram of a controller of a known tire information detecting system; and

FIG. 6 is a schematic illustration of a circuit diagram of a transponder of a known tire information detecting system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

An embodiment of the present invention is now herein described in detail with reference to the accompanying drawings. According to the present embodiment, like the above-described known tire information detecting system (wireless transmission system), a tire information detecting system includes a controller disposed on the body of a vehicle and a measured value transmitter (hereinafter referred to as a “transponder”) disposed in a tire.

In particular, the configuration of the transponder of the tire information detecting system according to the present embodiment is different from that of the known tire information detecting system. The circuit configuration of the transponder of the tire information detecting system according to the present embodiment is described below. The difference between the configurations of the controllers is described with reference to components shown in FIG. 5 as needed.

FIG. 1 illustrates an exemplary circuit configuration of the transponder of the tire information detecting system according to the present embodiment. Note that the circuit configuration shown in FIG. 1 is a simplified illustration. A low-pass filter L1/C1 included in the known transponder (see FIG. 6) is not shown. In FIG. 1 the low-pass filter is connected between an antenna 11 and a pair of coupling capacitors 13 and 15.

According to the present embodiment, as shown in FIG. 1, a transponder 10 includes the transmission/reception antenna 11. A modulating/demodulating diode 12 is connected to the antenna 11 in series. Additionally, a pressure resonator 14 is connected to the antenna 11 via the coupling capacitor 13. Furthermore, a reference resonator 16 is connected to the antenna 11 via the coupling capacitor 15.

The pressure resonator 14 and a reference resonator 16 are each composed of a quartz crystal resonating element. The pressure resonator 14 serves as a first resonator whereas the reference resonator 16 serves as a second resonator.

The pressure resonator 14 includes a quartz crystal resonating element 17a formed on a quartz piece 17 for measuring a pressure, a capacitor 18 for forming the load capacitance for determining the resonance frequency of the pressure resonator 14, and a capacitive pressure sensor (hereinafter simply referred to as a “pressure sensor”) 19. The pressure sensor 19 is connected to the quartz crystal resonating element 17a via an adjustment capacitor 20 so as to prevent the variation in detected values. The pressure resonator 14 has a resonance frequency of, for example, 9.800 MHz. This resonance frequency of the pressure resonator 14 varies in accordance with the tire pressure detected by the pressure sensor 19.

In contrast, the reference resonator 16 includes a quartz crystal resonating element 17b formed on the quartz piece 17 for providing a reference value for measuring a pressure, and a capacitor 21 for forming the load capacitance for determining the resonance frequency of the reference resonator 16. The reference resonator 16 serving as a reference sensor unit has a resonance frequency of, for example, 9.803 MHz.

The pressure resonator 14 is connected to the antenna 11 via the coupling capacitor 13. The reference resonator 16 is connected to the antenna 11 via the coupling capacitor 15. Accordingly, the affect of one of the pressure resonator 14 and the reference resonator 16 on the other is reduced to a level at which the measurement can be performed without any problems. Therefore, the resonance frequency of the reference resonator 16 is not affected by the pressure detected by the pressure sensor 19. The resonance frequency of the pressure resonator 14 is affected by not only the capacitance of the pressure sensor 19 that changes in accordance with the air pressure of a tire, but also an environmental change in the tire (e.g., a temperature change in the tire). By disposing the reference resonator 16 having no pressure sensor 19 and measuring the resonance frequency of the reference resonator 16, only the effect of the environmental change can be measured. Thus, the pressure sensor 19 can measure the tire pressure without the affect of the environmental change from the resonance frequencies of the two resonators.

As shown in FIG. 1, the quartz crystal resonating element 17a of the pressure resonator 14 and the quartz crystal resonating element 17b of the reference resonator 16 are formed from the same quartz piece 17. To form the quartz piece 17, two electrodes for the quartz crystal resonating elements 17a and 17b are evaporated on a single quartz piece. The electrode for the quartz crystal resonating elements 17a is connected to the pressure resonator 14 whereas the electrode for the quartz crystal resonating elements 17b is connected to the reference resonator 16. Since the two electrodes are evaporated on the same quartz piece, the characteristics including the temperature characteristic and the time degradation characteristic of the pressure resonator 14 can be made close to those of the reference resonator 16.

Unlike the known tire information detecting system, in the controller of the tire information detecting system according to the present embodiment, the oscillator G2 generates an oscillation signal having a frequency f2 that is close to the resonance frequency of the reference resonator 16 and an oscillation signal having a frequency f3 that is close to the resonance frequency of the pressure resonator 14. More specifically, an oscillation signal having a center frequency of 9.803 MHz and an oscillation signal having a center frequency of 9.800 MHz are generated. The carrier waves f1 are amplitude-modulated by these oscillation signals. The switch S1 selects whether the amplitude modulation is performed or not.

According to the present embodiment, amplitude modification is performed by the oscillation signal having a center frequency of f2 (the oscillation signal having a center frequency of 9.803 MHz) and, subsequently, the amplitude modification is stopped. Thereafter, amplitude modification is performed by the oscillation signal having a center frequency of f3 (the oscillation signal having a center frequency of 9.800 MHz) and, subsequently, the amplitude modification is stopped. Even when the amplitude modification by the first oscillation signal having a center frequency of f2 is stopped, the reference resonator 16 continues to oscillate for about 1 ms or more, like the known transponder. Accordingly, unmodulated carrier waves f1 are amplitude-modified by a signal having the resonance frequency of the reference resonator 16 via the diode 12 and then are emitted from the antenna 11. Similarly, even when the amplitude modification by the second oscillation signal having a center frequency of f3 is stopped, the pressure resonator 14 continues to oscillate for about 1 ms or more. Accordingly, unmodulated carrier waves f1 are amplitude-modified by a signal of the resonance frequency of the reference resonator 16 via the diode 12 and then are emitted from the antenna 11.

Since the reference resonator 16 and the pressure resonator 14 are disposed in the same tire, these resonance frequencies are affected by the temperature of the tire, in the same manner. In addition, the resonance frequency of the pressure resonator 14 is affected by a change in the pressure detected by the pressure sensor 19. In contrast, the resonance frequency of the reference resonator 16 is not affected by the change in the pressure detected by the pressure sensor 19. The controller receives the high-frequency signal amplitude-modified by the signal having the resonance frequency of the reference resonator 16 and the high-frequency signal amplitude-modified by the signal having the resonance frequency of the pressure resonator 14, which are affected in this manner. Subsequently, the controller determines the difference between the frequency of the signal having the resonance frequency retrieved from the former high-frequency signal (sometimes referred to as a “reference measurement frequency”) and the frequency of the signal having the resonance frequency retrieved from the latter high-frequency signal (sometimes referred to as a “pressure measurement frequency”). Thus, the controller measures the tire pressure. More specifically, a correlation data table among the reference measurement frequency, the pressure measurement frequency, and a tire pressure is generated in advance, and the tire pressure is computed using this correlation data table.

FIG. 2-4 are diagrams illustrating computation of tire pressure according to the difference between the reference measurement frequency and the pressure measurement frequency. The tire pressure can be detected by measuring a frequency difference between the reference measurement frequency and the pressure measurement frequency. That is, by computing the frequency difference between the pressure measurement frequency that is detected by the pressure sensor 19 (which is affected by a change in pressure) and the reference measurement frequency (which is not significantly affected by the change in pressure), the tire pressure can be accurately obtained.

Note that both the reference resonator 16 and the pressure resonator 14 are affected by the temperature of the tire, Accordingly, for example, when the temperature of the tire is changed, the center frequencies of the reference measurement frequency f2 and the pressure measurement frequency f3 deviate by substantially the same frequency width Δ, as illustrated by a dotted curve in FIG. 2 (see a reference measurement frequency f2′ and a pressure measurement frequency f3′ shown in FIG. 2). In particular, according to the present embodiment, the characteristics of the quartz crystal resonating element 17a used for the pressure resonator 14 closely resemble those of the quartz crystal resonating element 17b used for the reference resonator 16, as described below. Therefore, the difference between frequency changes caused by the change in temperature is small. Consequently, the frequency difference X between the reference measurement frequency f2 and the pressure measurement frequency f3 is substantially the same as the frequency difference X′ between the reference measurement frequency f2′ and the pressure measurement frequency f3′. Therefore, a measurement difference between the frequency difference X and the frequency difference X′ is negligible.

FIG. 3 illustrates a graph when the tire pressure and temperature are changed. The center frequency of the reference measurement frequency f2 deviates by a width Δ so that the reference measurement frequency f2 is changed to a reference measurement frequency f2″. In contrast, the center frequency of the pressure measurement frequency f3 deviates by the width Δ plus a width γ which is the affect of the pressure sensor 19 so that the pressure measurement frequency f3 is changed to a pressure measurement frequency f3″.

FIG. 4 illustrates a difference between a pressure measurement frequency and the reference measurement frequency. FIG. 4 indicates that, in any state, the frequency difference γ between the frequency difference X and the frequency difference X″ is affected only by the pressure. Therefore, the tire pressure can be obtained by using a formula or a correlation data table between this value and the tire pressure obtained through experimentation.

While, in the foregoing description, the tire pressure has been computed from a frequency difference, the tire pressure can be computed by measuring the temperature using the reference measurement frequency first and, subsequently, using the measured value of the pressure measurement frequency and a correlation data between a temperature and a pressure measurement frequency. That is, regardless of whether computed directly or indirectly, the tire pressure can be computed from the reference measurement frequency and the pressure measurement frequency.

Additionally, since the pressure resonator 14 and the reference resonator 16 are disposed in the same tire, these two resonators are affected by the environmental change, such as a temperature change, in the tire at the same time. In such a case, if the characteristics of the two quartz crystal resonating elements in the two resonators are different and the two quartz crystal resonating elements are affected by the same environmental change, the changes in the resonance frequencies of the pressure resonator 14 and the reference resonator 16 are different. As a result, an error occurs in computation of the tire pressure. The temperature characteristic is the most important among these characteristics. This is because, in general, quartz crystal resonating elements are sensitive to temperature variation, and a significant temperature change may occur in a tire. The main reason for providing the reference resonator 16 is to correct the affects of temperature variation. However, in this case, if the temperature characteristics of the quartz crystal resonating elements of the pressure resonator 14 and the reference resonator 16 are different, an error occurs in this correction. Therefore, the temperature characteristics are important. In addition, the time degradation characteristic must be considered to prevent an error.

Accordingly, the tire information detecting system according to the present embodiment employs the same quartz piece for the quartz crystal resonating elements of the pressure resonator 14 and the reference resonator 16. Thus, the characteristics of the pressure resonator 14 closely resemble the characteristics of the reference resonator 16. As a result, the above-described problem can be solved. Two electrodes are evaporated onto a single quartz piece to form the quartz piece 17. One of the two electrodes functions as an electrode of a first quartz crystal resonating element 17a of the pressure resonator 14 and the other of the two electrodes functions as an electrode of a second quartz crystal resonating element 17b of the reference resonator 16. One of the two quartz resonator resonates in accordance with a signal received from the controller and including two types of resonance frequencies. It is desirable that the vibration of the quartz piece in accordance with one of the two resonance frequencies is not transferred to the electrode of the quartz resonator that is not related to that resonance frequency

For example, the quartz piece on which the two electrodes are evaporated is resiliently separated by forming a groove or forming a border by means of laser between the two electrodes on the quartz piece 17, by forming a hole at the center between the two electrodes, or by increasing the distance between the two electrodes. In such a case, since vibrations in accordance with one of the two resonance frequencies received from the controller is not transferred to the electrode that is not related to that resonance frequency, the measured value, such as a tire pressure, can be precisely detected.

While the quartz crystal resonating elements 17a and 17b formed from a quartz crystal have been used as piezoelectric single-crystal resonating elements disposed in the pressure resonator 14 and the reference resonator 16, the piezoelectric single-crystal resonating elements are not limited to quartz crystal resonating elements. For example, a resonating element obtained by processing a piezoelectric single-crystal lithium tantalite (LiTaO₃), a piezoelectric single-crystal niobium tantalate (LiNbO₃), a piezoelectric single-crystal lithium borate (Li₂B₄O₇), a piezoelectric single-crystal potassium niobate (KNbO₃), a piezoelectric single-crystal langasite (La₃Ga₅SiO₁₄), a piezoelectric single-crystal langanite (La₃Nb_0.5Ga_5.5O₁₄), or a lead zinc niobate titanate single crystal can be used. Like the quartz crystal resonating element a plurality of these resonating elements can be produced from a wafer. In the manufacturing steps, two resonating elements having similar characteristics can be obtained on the same quartz piece. Therefore, these two resonating elements can be used as piezoelectric single-crystal resonating elements according to the present invention. To obtain similar characteristics in the manufacturing steps, the method used for the quartz crystal resonating element can be also used. However, the method is modified in accordance with the material. Since the quartz crystal resonating element has a high Q compared with the other piezoelectric single-crystal resonating elements, the response frequency is stable, and therefore, the measured values are stable. Accordingly, the quartz crystal resonating element is suitable for providing a high-precision tire information detecting system.

As described above, in the tire information detecting system according to the present embodiment, the transponder 10 includes the pressure resonator 14 that changes the resonance frequency thereof in accordance with a tire pressure and the reference resonator 16 having a resonance frequency that is unaffected by a change in the tire pressure. The controller computes a measured value on the basis of the resonance frequencies of the pressure resonator 14 and the reference resonator 16 based on resonance frequency signals of the pressure resonator 14 and the reference resonator 16. In this way, even when the temperature of the tire is changed, the measured value can be computed on the basis of the resonance frequencies of the two resonators affected by the change in the tire temperature. Thus, the affect of the tire temperature can be reduced, and therefore, the measured value of the tire pressure can be accurately obtained.

In particular, in the tire information detecting system according to the present embodiment, the piezoelectric single-crystal resonating elements, such as the quartz crystal resonating element included in the pressure resonator and in the reference resonator, are formed from the same single-crystal piece (quartz piece). Since the same single-crystal piece (quartz piece) is used for the pressure resonator and the reference resonator, the characteristics including the temperature characteristic and the time degradation characteristic of the pressure resonator can be made to be close to those of the reference resonator. As a result, even when the temperature of the tire changes, the affect of a change in the tire temperature is equally applied to the resonance frequencies of the two resonators. Accordingly, by computing the measured value in accordance with the frequency difference between the resonance frequencies of the pressure resonator and the reference resonator, the affects of tire temperature can be reduced. Therefore, the measured value of tire pressure can be further accurately obtained.

It should be noted that the present invention is not limited to the above-described embodiments. Various modifications can be made to the above-described embodiments. In the above-described embodiments, the sizes and shapes of the components shown in the attached drawings are not limited to those described. For example, the scale and dimensions may be altered within the spirit and scope of the inventive concepts described. In addition, various changes may be made within the spirit and scope of the present invention.

Furthermore, while the present embodiment has been described with reference to the controller in which the amplitude modification of the carrier waves f1 by the oscillation signal of 9.800 MHz is temporally shifted from that by the resonance signal of 9.803 MHz, the timing of the amplitude modification can be appropriately changed. For example, the amplitude modification of the carrier waves f1 by the oscillation signal of 9.800 MHz may be performed at the same time as that by the oscillation signal of 9.803 MHz. Even in such a case, the same advantage as that of the above-described embodiment can be provided.

Claims

1. A tire information detecting system comprising: a measured value transmitter disposed in a tire of a vehicle;a controller disposed in the body of the vehicle;the measured value transmitter further including an antenna;a modulation/demodulation unit connected to the antenna configured to modulate and demodulate signals received from and transmitted to the controller;first and second coupling capacitors connected to the antenna;a first resonator connected to the first coupling capacitor and including a first piezoelectric single-crystal resonating element and a pressure sensor, where the resonance frequency of the first resonator is changed in accordance with the pressure of the tire;a second resonator connected to the second coupling capacitor and including a second piezoelectric single-crystal resonating element and a capacitor, where the resonance frequency of the second resonator is not affected by the pressure of the tire;wherein the first piezoelectric single-crystal resonating element and the second piezoelectric single-crystal resonating element are formed on a single-crystal piece; andwherein the controller transmits a signal for resonating the first and second resonators, receives a signal modulated with the resonance frequency of the first resonator and a signal modulated with the resonance frequency of the second resonator, and computes a measured value in accordance with the resonance frequencies of the first and second resonators retrieved from the received signals.

2. The tire information detecting system according to claim 1, wherein the first piezoelectric single-crystal resonating element is a first quartz crystal resonating element, the second piezoelectric single-crystal resonating element is a second quartz crystal resonating element, and the single-crystal piece is a quartz piece.

3. The tire information detecting system according to claim 1, wherein an electrode for the first quartz crystal resonating element and an electrode for the second quartz crystal resonating element are attached to the quartz piece used for the quartz crystal resonating elements and wherein the quartz piece is elastically separated between the two electrodes.

4. The tire information detecting system according to claim 3, wherein a groove is formed between the two electrodes.

5. The tire information detecting system according to claim 3, wherein a hole is formed between the two electrodes.

6. A tire information detecting system comprising: a measured value transmitter disposed in a tire of a vehicle;a controller disposed in the vehicle;the measured value transmitter further including an antenna;a modulation/demodulation unit configured to modulate and demodulate signals received from and transmitted to the controller;a first resonator including a first piezoelectric single-crystal resonating element and a pressure sensor, where a resonance frequency of the first resonator is changed in accordance with a pressure of the tire;a second resonator including a second piezoelectric single-crystal resonating element, where a resonance frequency of the second resonator is not affected by a pressure of the tire;wherein the controller transmits a signal for resonating the first and second resonators, receives a signal modulated with the resonance frequency of the first resonator and a signal modulated with the resonance frequency of the second resonator, and computes a measured value in accordance with the resonance frequencies of the first and second resonators retrieved from the received signals.

7. The tire information detecting system according to claim 6, wherein the first piezoelectric single-crystal resonating element is a first quartz crystal resonating element, the second piezoelectric single-crystal resonating element is a second quartz crystal resonating element, and the single-crystal piece is a quartz piece.

8. The tire information detecting system according to claim 6, wherein an electrode for the first quartz crystal resonating element and an electrode for the second quartz crystal resonating element are attached to the quartz piece used for the quartz crystal resonating elements, wherein the quartz piece is disposed between the two electrodes.

9. The tire information detecting system according to claim 8, wherein a groove is formed between the two electrodes.

10. The tire information detecting system according to claim 8, wherein a hole is formed between the two electrodes.

11. A method for obtaining tire pressure data comprising: providing a measured value transmitter in a tire of a vehicle, the measured value transmitter further including an antenna, a modulation/demodulation unit configured to modulate and demodulate signals received from and transmitted to the controller, a first resonator including a first piezoelectric single-crystal resonating element and a pressure sensor, where a resonance frequency of the first resonator is changed in accordance with a pressure of the tire, a second resonator including a second piezoelectric single-crystal resonating element, where a resonance frequency of the second resonator is not affected by a pressure of the tire;transmitting a signal configured to cause the first and second resonators to resonate;receiving a signal modulated with the resonance frequency of the first resonator;receiving a signal a signal modulated with the resonance frequency of the second resonator; andcalculating a measured value in accordance with the resonance frequencies of the first and second resonators based on the received signals.

12. The method according to claim 11, wherein the first piezoelectric single-crystal resonating element is a first quartz crystal resonating element, the second piezoelectric single-crystal resonating element is a second quartz crystal resonating element, and the single-crystal piece is a quartz piece.

13. The method according to claim 11, wherein an electrode for the first quartz crystal resonating element and an electrode for the second quartz crystal resonating element are attached to the quartz piece used for the quartz crystal resonating elements, wherein the quartz piece is disposed between the two electrodes.

14. The method according to claim 13, including forming a groove between the two electrodes.

15. The method according to claim 13, including forming a hole between the two electrodes.