JP3075432B2 - Tire monitoring equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for monitoring tire pressure.

[0002]

2. Description of the Related Art Conventionally, as a tire monitoring device for monitoring tire pressure, there is known a tire monitoring device described in US Pat. No. 4,567,459. This device supplies power to the active circuit for pressure detection built in the tire from the vehicle body side,
The electric signal corresponding to the pressure is frequency-modulated and transmitted to the vehicle body by electromagnetic coupling.

Japanese Patent Application Laid-Open No. 61-141098 discloses a tire pressure detecting device of a resonance circuit type. That is, this device uses a pressure-sensitive sensor (for example, a semiconductor pressure-sensitive sensor) whose resistance value changes according to tire pressure and an LC resonance circuit,
A Q variable resonance circuit whose Q varies according to a change in tire pressure is provided on the rim side. Then, a fixed frequency alternating current is supplied to this Q variable resonance circuit from the fixed frequency oscillation circuit on the vehicle body side by electromagnetic coupling in a non-contact manner, and further, the Q variable resonance circuit is electromagnetically coupled to the Q variable resonance circuit. The tire pressure is detected for the change.

[0004]

However, in the device described in the above-mentioned U.S. Pat. No. 4,567,459, various semiconductor elements and ICs must be built in the tire, and such a severe tire environment, that is, high temperature, large It is not easy to use a semiconductor element or an IC under an acceleration environment in terms of a change in characteristics, a deterioration in life, and the like.

On the other hand, the apparatus disclosed in Japanese Patent Application Laid-Open No. 61-141098 has an advantage that the above-described semiconductor element and IC can be omitted. However, the Q of the Q variable resonance circuit built in the tire is different from the resistance value of the pressure-sensitive sensor. When a semiconductor pressure sensor is used as the pressure sensor, it is necessary to employ a semiconductor pressure sensor that can be used in a high-temperature environment as described above. Also, Japanese Patent Application Laid-Open No. 61-141098
In the device of the publication, for example, to transmit a plurality of types of tire signals, such as tire pressure and tire temperature, to the vehicle body side,
One electromagnetic coupling circuit must be prepared for each tire signal, and the structure is significantly complicated. Furthermore, when a plurality of electromagnetic coupling circuits are arranged close to each other, an adverse effect (for example, crosstalk) due to interference between adjacent electromagnetic coupling circuits occurs, and when they are arranged apart from each other, there is a problem in securing an installation space. .

The present invention has been made in view of the above problems, and has a tire monitoring device capable of detecting tire information stably even under changes in tire environment and capable of detecting a plurality of types of tire signals with a simple configuration. Its purpose is to provide a device.

[0007]

SUMMARY OF THE INVENTION A tire monitoring apparatus according to the present invention is disposed on a rim side having a plurality of resonance frequencies, each resonance frequency being a function of a plurality of state variables of a tire. And at least one vehicle-body-side coil disposed on the vehicle body and electromagnetically coupled to the resonance circuit in a non-contact manner, and a frequency-variable alternating current supplied to the resonance circuit through the vehicle-body-side coil disposed on the vehicle body side. Frequency variable current feeding means, a resonance frequency detecting means disposed on the vehicle body side for detecting a resonance frequency of the resonance circuit through the vehicle body side coil, and calculating a state variable of the tire from the detected resonance frequency. And state variable calculating means.

[0008] In a preferred aspect, the vehicle body side coil includes an excitation coil connected to the frequency variable current supply means and a reception coil connected to the resonance frequency detection means. In another aspect, the vehicle body side coil can serve as both the excitation coil and the reception coil. In a preferred aspect, the resonance circuit is configured by connecting an LC series circuit unit, a capacitor, and an inductance in parallel.

[0009] The variable frequency current supply means may supply an AC voltage whose frequency can be continuously changed, or may supply an AC voltage whose frequency changes discretely. The resonance circuit of the present invention can employ not only an LC resonance circuit including a reactance element and a capacitance element but also a complex impedance element such as a piezoelectric element, and can naturally include a resistance component.

The state variables of the tire include, for example, tire pressure and air temperature in the tire.

[0011]

When the variable frequency current supply means supplies a variable frequency alternating current to the rim side resonance circuit through the vehicle body side coil in a non-contact manner by electromagnetic coupling, the resonance circuit is excited and the resonance frequency of the resonance circuit is supplied to the vehicle body side coil side. Are induced in a non-contact manner by electromagnetic coupling, and the resonance frequency detecting means detects the resonance frequency of the resonance circuit based on the resonance current component.

In particular, in the present invention, since the resonance circuit has a plurality of resonance frequencies, and each resonance frequency is a function of a plurality of tire state variables, the state variable calculation means calculates the tire state variables from each resonance frequency. calculate.

[0013]

As described above, the tire monitoring device of the present invention supplies a resonance circuit having a plurality of resonance frequencies each of which is a function of a plurality of tire state variables, and supplies a frequency-variable alternating current to the resonance circuit. Frequency variable current supply means, a resonance frequency detection means for detecting a resonance frequency of the resonance circuit, and a state variable calculation means for calculating a tire state variable from the detected resonance frequency, so that a semiconductor element weak to heat, A plurality of tire state variables can be detected on the vehicle body side in a non-contact manner by the rim side circuit having a simple configuration without incorporating the IC in the tire.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a schematic view showing the entire configuration of a first embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA of FIG. 1 and 2, reference numeral 1 denotes a wheel of a tire, and reference numeral 3 denotes a rim connected to the wheel 1. Reference numeral 5 denotes a fixing case made of an elastic material such as beryllium copper. Both ends of the fixing case 5 are fitted into the cutout portions 7 of the rim 3, and the fixing case 5 is an elastic material such as beryllium copper. Therefore, the notch 7 is fitted by the elastic force.
The notch 7 may be joined by welding or bonding. Reference numeral 9 denotes a pressure / temperature detecting unit (a part of the resonance circuit according to the present invention), which is fixed to the fixed case 5 in a state of not contacting the rim 3. The terminal of the pressure / temperature detecting section 9 is connected to a coil 13 on the rim side via a lead wire 11.
It is connected to the.

Reference numeral 15 denotes an insulating member such as glass, and two conductors are embedded in the insulating member 15. After fixing the insulating member 15 having such two conductors to the rim 3,
After the lead wire 11 is connected to the embedded conductor, it is sealed with a rubber seal 17. Reference numeral 19 denotes a short cylindrical bobbin with a flange, on which the rim-side coil 13 is wound.
1 and the outer peripheral surface of the bobbin mounting stay 21 is welded or adhesively fixed to the inner peripheral surface of the rim 3.

Reference numeral 23 denotes a coil mounting stay fixed to the vehicle body (not shown), which is fixed to the vehicle body by a stay mounting hole 25 and a bolt (not shown). The distal end of the coil mounting stay 23 extends to a position close to the inner peripheral surface of the bobbin 19, and the distal end of the coil mounting stay 23 has a case made of a non-magnetic material such as aluminum.
The bolt 39 is attached by a bolt 41.

As shown in FIG. 2, the case 39 accommodates iron cores 29a and 29b. The iron core 29a has an excitation coil (body-side coil in the present invention) 99 and the iron core 29.
b is a receiving coil 101 (body-side coil in the present invention)
Is wound. Both coils 99 and 101 are separated by a separator 97 made of a magnetic material, and both ends of the exciting coil 99 and the receiving coil 101 are connected to a lead wire 31.
And an electronic control unit (hereinafter, referred to as an ECU) 35 via the.

The ECU 35 constitutes the variable frequency current supply means 33, the resonance frequency detecting means 34 and the state variable calculating means 38 according to the present invention. Next, details of the vicinity of the fixed case 5 will be described with reference to FIGS. In FIG. 3, reference numeral 5a denotes a bending and fixing part, and the bending and fixing part 5a integrated with the fixing case 5 is fitted to the pressure / temperature detecting part 9. FIG. 4 is a plan view of FIG. In FIG. 4, reference numeral 43 denotes a harness member for fixing the lead wire 11.

Next, the pressure / temperature detecting section 9 of this embodiment will be described with reference to FIG. The pressure / temperature detecting section 9 includes a pressure detecting section 9a (see FIG. 5) and a temperature detecting section 9b (see FIG. 6).
And a series capacitor 55 (see FIG. 7).
The pressure detecting section 9a includes a cup-shaped case 90, a diaphragm 91 for sealing the opening of the case 90 to form a closed space S inside the case 90, and a root fixed at the center of the diaphragm 91. A ferromagnetic rod 92 having a distal end extending into the closed space S and a cylindrical yoke 93 made of a ferromagnetic substance having openings formed at both ends thereof into which the ferromagnetic rod 92 is slidably inserted.
And a coil 54 housed in a cylindrical yoke 93. The cylindrical yoke 93 constitutes a gap magnetic circuit. When the tire pressure changes, the ferromagnetic rod 92 displaced by the diaphragm 91 changes the gap length d of the magnetic circuit, thereby changing the inductance L of the coil 54.

The temperature detecting section 9b (see FIG. 6) comprises a thin dish-shaped metal case 95 and a lid plate 96 for closing the opening of the case 95 to form a closed space M inside the case 95. And the lid plate 96
And a piezoelectric capacitor 53 fixed so as to be electrically insulable with an insulating film (not shown) interposed therebetween. The piezoelectric capacitor 53 is a barium titanate-based complex impedance element. However, in the frequency band used in this embodiment, the admittance component is dominant, so that it is considered as a simple capacitor. Since the capacity of the piezoelectric capacitor 53 is in the closed space M, it is not affected by the tire pressure, but only fluctuates by the air temperature in the tire transmitted through the metal case 95 and the cover plate 96.

FIG. 7 shows an equivalent circuit of the device of this embodiment. Piezoelectric capacitor 53 and coil 5 of pressure temperature detecting section 9
4 and the series capacitor 55 together with the rim-side coil 13 constitute the resonance circuit 100 according to the present invention. Specifically, the coil 54 and the series capacitor 55 which are connected in series to form an LC A piezo-electric capacitor 53 is connected to both ends of the rim-side coil 13.

This resonance circuit 100 has two resonance frequencies f
1, f2, which are defined by the following equations (1) and (2). However, L ₁ is the inductance of the rim-side coil 13, the inductance of L ₂ is the coil 54, C ₁
Is the capacitance of the piezoelectric capacitor 53 for detecting the tire temperature,
C ₂ is the capacitance of the series capacitor 55.

[0023]

[Equation 1] _{f1 = (A / 2L 1 L} 2 C 1 C 2) 1/2 / 2Π A = {(L 2 C 2 - (C 1 + C 2) L 1) 2 + 4L 1 L 2 C 2 2} ^{_{1/2 + L 2 C 2 + (}} C 1 + C 2) L 1

[0024]

[Equation 2] _{f2 = (B / 2L 1 L} 2 C 1 C 2) 1/2 / 2Π B = - {(L 2 C 2 - (C 1 + C 2) L 1) 2 + 4L 1 L 2 C 2 2 ｝ ^1/2 + L ₂ C ₂ + (C ₁ + C ₂ ) L ₁ As can be seen from Equations 1 and 2, the two resonance frequencies f1 and f2 of the resonance circuit 100 are represented by impedances L ₁ , L ₂ , Since it is a function of C ₁ and C ₂ , if two impedances arbitrarily selected from L ₁ , L ₂ , C ₁ and C ₂ are variables that change depending on the tire state variable, respectively, the resonance frequency f 1, When f2 is detected, Equation 1 is obtained.
It can be seen that by solving ₂ , the above two variables among L ₁ , L ₂ , C ₁ , and C ₂ can be calculated. As described above in this embodiment, a C ₁ to a variable of a tire temperature, and the L ₂ as a variable of the tire pressure. Furthermore, the tire temperature from C ₁ obtained, can be calculated tire pressure from L _2.

The excitation coil 99 is supplied with an alternating current of variable frequency from the ECU 35, and supplies the alternating current to the resonance circuit 100 by non-contact electromagnetic coupling with the rim side coil 13. An alternating current is induced in the receiving coil 101 from the resonance circuit 100 by non-contact electromagnetic coupling with the rim-side coil 13. In this circuit, the excitation frequency, that is, the frequency of the excitation voltage V1 applied to the excitation coil
It is known that the phase difference between the excitation voltage V1 and the reception voltage V2 becomes π / 2 when the resonance frequency is equal to (see FIG. 8). Therefore, the frequency of the excitation voltage V1 is adjusted so that the phase difference between the excitation voltage V1 and the reception voltage V2 becomes π / 2, and the frequency value of the reception voltage V2 when the phase difference is π / 2 is detected as the resonance frequency fr. I just need. In particular, the resonance circuit 1
When 00 is in the resonance state, the reception voltage V2 of the reception coil 101 becomes the maximum, so that the SN ratio of the reception voltage V2 increases, and the detection accuracy also improves. The excitation coil 99
The electromagnetic coupling between the power supply and the receiving coil 101 is ignored here.

FIG. 9 shows an example of the ECU 35, and FIG. 10 shows waveforms at various parts of the ECU 35. The voltage controlled oscillator (hereinafter abbreviated as VCO) 206 is designed to be able to oscillate within a range including the two resonance frequencies f1 and f2 of the resonance circuit 100, and the output voltage V1 of the VCO 206 is output to the rim via the excitation coil 99. It is radiated to the side coil 13. Thereby, the resonance circuit 100 is excited, and an induced electromotive force V <b> 2 is generated at both ends of the receiving coil 101 by the electromagnetic wave radiated from the rim-side coil 13. At this time, the waveform of the reception voltage V2 of the reception coil 101 is a sine wave. The waveform of the reception voltage V2 is a rectangular wave voltage V having the same phase as the reception voltage V2 by the comparator 201.
k at the exclusive OR gate 202.
This is compared with the output voltage V1 of O206. As shown in FIG. 10, the output voltage Vg of the exclusive OR gate 202 is shown.
Goes low if the states of Vk and V1 are equal, and goes high if they are different. Exclusive OR gate 202
The output voltage Vg is converted by a low-pass filter 203 into a DC voltage Vf having a different level depending on the duty ratio, and the DC voltage Vf is compared with a reference voltage Vr from a reference voltage generator 204 in a control voltage generator 205. Is done.

The control voltage generator 205 controls the output voltage Vc so that the difference voltage between the DC voltage Vf and the reference voltage Vr becomes zero.
And the VCO 206 outputs a rectangular wave having a frequency uniquely determined by the value of the output voltage Vc. Here, if the phase difference between the output signal Vk of the comparator 201 and the output signal V1 of the VCO 206 is π / 2, the duty ratio of the output voltage Vg of the exclusive OR gate 202 is 0.5. Therefore, the output voltage Vf of the low-pass filter 203 at this time is half the peak value Vgx of the output voltage Vg of the exclusive OR gate 202. Therefore, by making the value of the reference voltage Vr output from the reference voltage generator 204 half of the output voltage Vg of the exclusive OR gate 202, the oscillation frequency of the VCO 206 always becomes the resonance frequency of the resonance circuit.

Here, the microcomputer 209 determines the resonance frequency f1
Is detected, the control voltage generator 205 supplies the first voltage Vc.
1 and the control voltage generator 205 outputs this first voltage Vc1 to the voltage controlled oscillator 206 regardless of the voltages Vr and Vf by the built-in gate (not shown), and the voltage controlled oscillator 206 outputs the first voltage Vc1. Oscillates at a frequency corresponding to the voltage Vc1.
The first voltage Vc1 is set near the first resonance frequency f1 of the resonance circuit 100, and as a result, the control voltage generator 205 is driven by a built-in gate (not shown) to generate the first voltage Vc1.
When the output of c1 is cut off and the output voltage Vc is output so that the difference voltage between the DC voltage Vf and the reference voltage Vr becomes 0, the voltage controlled oscillator 206 oscillates at the first resonance frequency f1.

Similarly, the microcomputer 209 determines that the resonance frequency f2
Is detected, the control voltage generator 205 supplies the second voltage Vc.
2 and the control voltage generator 205 outputs the second voltage Vc2 to the voltage controlled oscillator 206 regardless of the voltages Vr and Vf by the built-in gate (not shown), and the voltage controlled oscillator 206 outputs the second voltage Vc2. Oscillates at a frequency corresponding to the voltage Vc2.
This second voltage Vc2 is set in the vicinity of the second resonance frequency f2 of the resonance circuit 100. As a result, the control voltage generator 205 is driven by a built-in gate (not shown) to generate the second voltage Vc2.
When the output of c2 is cut off and the output voltage Vc is output so that the difference voltage between the DC voltage Vf and the reference voltage Vr becomes 0, the voltage controlled oscillator 206 oscillates at the second resonance frequency f2.

Next, the first,
Inductance C associated with inductance L ₂ and tire temperature associated from the second resonance frequency f2 in the tire pressure
_The process for finding ₂ will be described. Voltage controlled oscillator 206
The oscillation voltage V1 is pulse-shaped by the Schmitt trigger 207, input to the counter 208 and counted, and the count value is sent to the microcomputer 209 as appropriate.

FIG. 11 shows the resonance frequency f of the microcomputer 209.
1 shows an f2 detection routine. First, the control voltage generator 2
The first voltage Vc1 is output at 05 (102). Then
The voltage controlled oscillator 206 oscillates at the first resonance frequency f1,
Thereafter, the control voltage generator 205 cuts off the first voltage Vc1, and as a result, the voltage controlled oscillator 206 oscillates at the first resonance frequency f1.

The voltage controlled oscillator 206 has a first resonance frequency f
The microcomputer 209 waits for the time ΔT until it oscillates at 1 (104), and then reads the first resonance frequency f1 from the counter 208 (106). More specifically, the count value C1 of the counter 208 at a certain time is read, and then, after a certain time delay, the count value C2 is read again to calculate the difference C2−C1.

Next, the second voltage V is applied to the control voltage generator 205.
c2 is output (108). Then, the voltage controlled oscillator 2
06 oscillates at the second resonance frequency f2, after which the control voltage generator 205 cuts off the second voltage Vc2, so that the voltage controlled oscillator 206 oscillates at the second resonance frequency f2.
The microcomputer 209 waits for the time ΔT until the voltage controlled oscillator 206 oscillates at the second resonance frequency f2 (11
0), and then the counter 208 outputs the second resonance frequency f2
Is read (112).

Next, the microcomputer 209 calculates L ₂ and C ₁ based on the resonance frequencies f 1 and f ₂ with reference to the built-in map (114), and refers to the built-in map from the calculated L ₂ and C ₁ . Then, the tire pressure and the tire temperature are searched (116). (Embodiment 2) FIG. 12 shows another modified embodiment of the ECU 35, and FIG. 13 shows signal waveforms of the respective parts.

An electromagnetic wave radiated from the VCO 304 toward the rim-side coil 13 via the excitation coil 99 excites the resonance circuit 100. At this time, the electromagnetic wave radiated from the rim-side coil 13 is induced at both ends of the receiving coil 101. Generates power. The reception voltage V2 of the reception coil 101 is
1 is converted into a rectangular wave voltage Vk having the same phase as the reception voltage V2,
The signal is input to the input terminal D of the D-type flip-flop 302. The clock pulse input terminal CK of the D-type flip-flop 302 is connected to the VCO 30
4, a signal voltage Vck having a phase different from that of the output voltage V1 by π / 2 is input.

As shown in FIG. 13, the 90-degree phase shifter 3
05 when the signal voltage Vck rises.
Is high level, that is, the rectangular wave voltage V
If k is ahead of the signal voltage Vck in phase, the output voltage Vg of the D-type flip-flop 302 goes high. If the rectangular wave voltage Vk is at a low level when the signal voltage Vck of the 90-degree phase shifter 305 rises, that is, if the phase of the rectangular wave voltage Vk is delayed from the signal voltage Vck, the D-type flip-flop The output voltage Vg of 302 becomes low level. The output voltage Vg of the D-type flip-flop 302 is converted to a direct current by the low-pass filter 303 and input to the VCO 304, and the VCO 304 oscillates at a frequency corresponding to the output voltage Vc of the low-pass filter 303.
The output voltage Vc of the low-pass filter 303 is a D-type flip-flop.
When the output voltage Vg of the flop 302 switches from high level to low level, it gradually decreases, and when it switches from low level to high level, it gradually increases. As a result, V
The oscillation frequency of the CO 304 increases and decreases as the output voltage Vc of the low-pass filter 303 increases and decreases.

Here, as shown in FIG.
1 and the output voltage V of the VCO
1 or the phase difference Δθ2 between the rectangular wave voltage Vk and the output voltage Vck of the 90-degree phase shifter 305 decreases monotonically with the frequency near the resonance frequency fr of the resonance circuit. Therefore, when the phase of the rectangular wave voltage Vk is ahead of the output voltage Vck of the phase shifter 305 by 90 degrees, the output voltage Vc of the low-pass filter 303 increases, the oscillation frequency of the VCO 304 increases, and the rectangular wave voltage Vk becomes 90 degrees. Phase shifter 30
5, the phase difference goes to zero.

Conversely, when the phase of the rectangular wave voltage Vk is behind the output voltage Vck of the 90-degree phase shifter 305, the output voltage Vc of the low-pass filter 303 decreases, and the oscillation frequency of the VCO 304 decreases. Vk and 90 degree phase shifter 3
The phase difference between the output voltage Vck and the output voltage 05 becomes zero. After all, in this circuit, the rectangular wave voltage Vk output from the comparator 301 and the output voltage Vc of the 90-degree phase shifter 305
The operation is performed such that the phase difference Δθ2 between the first and second k is set to zero.

As shown in FIG. 13, since the phase of the output voltage Vck of the 90-degree phase shifter 305 leads the output voltage V1 of the VCO 304 by π / 2, the rectangular wave voltage Vk
Is always π / 2, and the oscillation frequency of the VCO 304 is fixed to the resonance frequency of the resonance circuit 100. Also in the circuit of FIG. 12, a switching gate 306 is provided between the low-pass filter 303 and the voltage controlled oscillator 304, and the first and second voltages Vc1 and Vc are connected to one input terminal of the switching gate 306.
By inputting c2 and setting the initial oscillation frequency of the voltage controlled oscillator 304 to each of the vicinity of the first resonance frequency f1 or the second resonance frequency f2, the resonance frequency f
1, f2 can be obtained.

As described above, in this embodiment, the resonance circuit 3 has a plurality of resonance frequencies, and each resonance frequency f
Since 1 and f2 are two-variable functions of the tire pressure and the tire temperature, respectively, the electromagnetic coupling system can be one system, and excellent effects such as simplification of the configuration and improvement of the SN ratio can be achieved. it can. FIGS. 15 to 17 show the results of calculation of the resonance frequencies f1 and f2 of the resonance circuit (see FIG. 7) 100. FIG.

FIG. 15 shows the basic state, where L ₁ = 2.4 m.
H, L ₂ = 30 mH, C ₁ = 8,000 pF, C ₂ =
This is the case where 2,400 pF is set. FIG. 16 shows a case where only C ₁ is changed and C ₁ = 1600 pF. FIG.
7 shows a case where changing only L _2, and the L ₂ = 30 mH. From the figure, it has a resonance frequency of the resonance circuit 100 is two points shown in the figure, they it can be seen that changing the value of C ₁ or L _2.

Of course, L ₁ and C ₂ may be changed instead of L ₂ and C ₁ . It is also possible to adopt another type of resonance circuit having a plurality of resonance frequencies. FIG.
Shows the measured results. Here, L ₁ = 2.3 m
H, L ₂ = 3.6 mH, C ₁ = 10,000 pF, C ₂
= 22,000 pF.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part showing an entire configuration of a first embodiment of the present invention;

FIG. 2 is a sectional view taken along line AA of FIG. 1;

FIG. 3 is a schematic diagram showing an attached state of a pressure detection unit according to the first embodiment;

FIG. 4 is a plan view of FIG. 3;

FIG. 5 is a cross-sectional view of a pressure detection unit in the pressure / temperature detection unit.

FIG. 6 is a cross-sectional view of a temperature detection unit in the pressure / temperature detection unit.

FIG. 7 is an equivalent circuit diagram of the first embodiment,

FIG. 8 is a graph showing the relationship between the output level and the phase difference of the resonance circuit and the frequency;

FIG. 9 is a block circuit diagram of an ECU according to the first embodiment;

10 is a signal waveform diagram of each part of the ECU of FIG. 9;

FIG. 11 is a flowchart showing a tire pressure and temperature detecting operation of a microcomputer in the ECU of FIG. 9;

FIG. 12 is a block circuit diagram of an ECU of a second embodiment, a characteristic diagram showing a relationship between a current flowing through the ECU and an excitation frequency,

13 is a signal waveform diagram of each part of the ECU of FIG. 12,

FIG. 14 is a characteristic diagram showing a relationship between a phase difference and an oscillation frequency;

FIG. 15 is a calculation graph showing the relationship between the output level and the phase difference of the resonance circuit and the frequency for indicating the resonance characteristics of the resonance circuit of FIG. 7;

FIG. 16 is a calculation graph showing the relationship between the output level and the phase difference of the resonance circuit and the frequency for indicating the resonance characteristics of the resonance circuit of FIG. 7;

17 is a calculation graph showing the relationship between the output level and the phase difference of the resonance circuit and the frequency for showing the resonance characteristics of the resonance circuit of FIG. 7;

18 is an actual measurement graph showing the relationship between the output level and the phase difference of the resonance circuit and the frequency for showing the resonance characteristics of the resonance circuit of FIG. 7;

[Explanation of symbols]

100 is a resonance circuit, 99 is an excitation coil (body-side coil), 101 is a reception coil (body-side coil), and 35 is E
CU (frequency variable current supply means, resonance frequency detection means,
State variable calculation means),

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Chita Tojo 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Co., Ltd. (72) Inventor Masaru Suzuki 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Japan Denso Stock In-house (56) References JP-A-3-5900 (JP, A) JP-A-2-162222 (JP, A) JP-A-61-141098 (JP, A) JP-A-4-254730 (JP, A) JP-A-4-212611 (JP, A) JP-A-57-197694 (JP, A) JP-A-61-136198 (JP, A) JP-A-61-177826 (JP, A) JP-A-59-197826 47850 (JP, A) Japanese Utility Model 2-116395 (JP, U) Japanese Utility Model 1-147706 (JP, U) Japanese Utility Model 51-15949 (JP, U) Japanese Utility Model 5-22244 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) G01L 17/00 B60C 23/02 G08C 19/00

Claims (3)

(57) [Claims] 1. A resonance circuit having a plurality of resonance frequencies disposed on a rim side, wherein each of the resonance frequencies is a function of a plurality of state variables of a tire, and a resonance circuit disposed on a vehicle body side. At least one vehicle body side coil that is electromagnetically coupled to the vehicle body in a non-contact manner, frequency variable current supply means provided on the vehicle body side, and supplying a variable frequency alternating current to the resonance circuit through the vehicle body side coil; A resonance frequency detection unit that detects a resonance frequency of the resonance circuit through the vehicle body side coil; anda state variable calculation unit that calculates a state variable of the tire from the detected resonance frequency. Tire monitoring device. 2. The tire monitoring device according to claim 1, wherein the vehicle body side coil includes an excitation coil connected to the variable frequency current supply means, and a reception coil connected to the resonance frequency detection means. 3. The tire monitoring device according to claim 1, wherein the resonance circuit is configured by connecting an LC series circuit unit, a capacitor, and an inductance in parallel.