JPH06281521A - Method for adjusting pressure sensor - Google Patents

Abstract

PURPOSE:To realize an adjusting method for high sensitivity pressure sensor having small output change due to the surrounding environment. CONSTITUTION:When a diaphragm 93c displaces due to the pressure difference of fluid working on both sides of the diaphragm 93c, the gap size (hereinafter referred to gap length) between a magnetic film 93d put on the diaphragm 93c and a coil 92 adjacent to the magnetic film 93d varies and by this, the inductance of a coil 92 varies. A circuit part supplies the coil 92 with alternating current and also detects the signal component modulated by the impedance variation in the coil in accordance with the above pressure difference. A plurality of slits formed on the magnetic film 93d with specific intervals in parallel to the magnetic flux penetration direction acts to reduce eddy current and resultingly increase the current variation due to gap variation (pressure variation) and therefore improve the detection sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pressure sensor, for example, a pressure sensor for detecting tire air pressure.

[0002]

2. Description of the Related Art Conventionally, as a sensor of this kind, Japanese Patent Laid-Open No.
There is one disclosed in Japanese Patent No. 124771. A diaphragm or a bellows which is displaced by a pressure difference changes the electrostatic capacity of a piezoelectric element, and the electrostatic capacity is converted into an electric signal to change the electrostatic capacity. Is detected.

A pressure sensor is also known in which a piezoresistive element is arranged on the diaphragm to detect a pressure change as a change in electric resistance.

[0004]

However, in the capacitance type pressure sensor described above, the material characteristic of the piezoelectric element is a main parameter that governs the detection sensitivity, that is, the pressure-capacitance characteristic. The problem is that manufacturing variations cause sensitivity variations.

A piezoresistive pressure sensor such as a semiconductor pressure sensor has the same problem. In view of the above problems, the inventors of the present invention change the gap length of a magnetic circuit with a gap by using a magnetic film attached to a diaphragm that is displaced by a pressure change, and change the magnetic resistance of the magnetic circuit as the inductance of the coil. I applied for a pressure sensor for detection (Japanese Patent Application No. 5-36282).

In this pressure sensor, although the variation in sensitivity due to the variation in material characteristics is small, an amorphous magnetic film or a permalloy film, which is suitable as a magnetic film and has a small hysteresis loss, has a relatively low electric resistance, which is advantageous for improving the SN ratio. Large eddy current loss occurs in the high frequency range.
Considering the equivalent electric circuit, this increase in eddy current loss becomes a parallel resistance component with respect to the coil inductance component, which is a detection parameter, and reduces the rate of change in the output current due to a gap change, which reduces detection sensitivity. There is.

The present invention has been made in view of this problem, and an object thereof is to provide a pressure sensor which realizes high sensitivity by reducing the eddy current loss of the magnetic film.

[0008]

The pressure sensor of the present invention comprises:
A pressure sensor including a case, a diaphragm whose peripheral portion is supported by the case and which is displaced according to a pressure difference between two fluids acting on both surfaces of the central portion, and a conversion portion which converts the displacement of the diaphragm into an electric signal. In the above-mentioned, the conversion part is arranged on the diaphragm and has a high magnetic permeability, and the size of the gap based on the displacement of the diaphragm, which is held in the case in close proximity to the magnetic film via a predetermined gap. And a circuit section for feeding an alternating current to the coil to detect a signal component modulated by the inductance, wherein the magnetic film has a predetermined interval in parallel with a magnetic flux flow direction. It is characterized by having a plurality of slits formed in.

In a preferred embodiment, a magnetic circuit having a gap is formed with the magnetic film so as to face each other in a predetermined region of the magnetic film via a minute gap, and the magnetic film has a magnetic core wound with a coil. The slit is formed in a region where magnetic flux flows from the magnetic core.

[0010]

When the diaphragm is displaced by the pressure difference of the fluid acting on both sides of the diaphragm, the size of the gap between the magnetic film on the diaphragm and the coil adjacent to this magnetic film (hereinafter referred to as the gap length). ) Changes, which changes the inductance of the coil.

The circuit section supplies an alternating current to the coil and detects a signal component modulated by the change in the coil inductance according to the pressure difference. A plurality of slits formed in the magnetic film at predetermined intervals in parallel with the magnetic flux flow direction,
By reducing the eddy current, the current change due to the gap change (pressure change) is increased, and the detection sensitivity is improved.

As described above, the pressure sensor of the present invention detects the magnetic film with a slit arranged on the diaphragm, the coil arranged close to this magnetic film, and the inductance of this coil. Since it is provided with the circuit section, it is possible to realize a highly sensitive pressure sensor with little change in output due to the surrounding environment.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings. (Embodiment 1) FIG. 1 is an overall configuration diagram showing an embodiment of a tire monitoring apparatus using a pressure sensor of the present invention, and FIG. 2 is a sectional view taken along line AA.

In FIGS. 1 and 2, reference numeral 1 is a wheel of the tire, and 3 is 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 which are fitted in the notch 7 of the rim 3, and the fixing case 5 is an elastic material such as beryllium copper. Therefore, the elastic force fits the notch 7. Note that the notch 7 may be joined by welding or adhesion. Reference numeral 9 is a pressure / temperature detector, which is fixed to the rim 3 in a fixed case 5 in a non-contact state.
It is fixed to. The terminal of the pressure / temperature detector 9 is connected to the rim-side coil 13 via a lead wire 11.

Reference numeral 15 denotes an insulating member such as glass. Two insulating wires are embedded in the insulating member 15. After fixing the insulating member 15 having such two conductive wires to the rim 3,
After the lead wire 11 is connected to the embedded conductive wire, it is sealed by a rubber seal 17. Reference numeral 19 is a short cylindrical bobbin with a flange, the rim-side coil 13 is wound around the bobbin 19, and the bobbin 19 is a bobbin mounting stage-2.
1 is fixed to the inner peripheral surface of the rim 3, and the outer peripheral surface of the bobbin mounting stage 21 is welded or fixed to the inner peripheral surface of the rim 3.

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

As shown in FIG. 2, iron cores 29a and 29b are housed in the case 39. An exciting coil 99 is wound around the iron core 29a and a receiving coil 101 is wound around the iron core 29b. Both coils 99 and 101 are partitioned by a separator 27 made of a non-magnetic material, and both ends of the exciting coil 99 and the receiving coil 101 are electronically controlled by a lead wire 31 (hereinafter referred to as ECU). It is connected to 35.

Next, referring to FIG. 3 and FIG.
The details of the vicinity will be described. In FIG. 3, reference numeral 5a denotes a bending fixing portion, and the bending fixing portion 5a integrated with the fixing case 5 is fitted to the pressure temperature detecting portion 9. Figure 3
A plan view of is shown in FIG. In FIG. 4, 43 is a lead wire 1
1 is a harness member for fixing 1.

Next, the pressure / temperature detector 9 will be described with reference to FIG. The pressure / temperature detector 9 is a pressure detector (EC
A pressure sensor according to the present invention, together with U (circuit portion according to the present invention) 35, 9a (see FIG. 5) and a temperature detecting portion 9
b (see FIG. 6) and a series capacitor 55 (see FIG. 7). 5, the pressure portion detection portion 9a includes a ferrite core 91 having a partially bottomed cylindrical shape, which will be described later, in which a concave portion 90 having an upper end opening is provided, and a coil 92 accommodated in the concave portion 90.
And a hollow disk-shaped diaphragm portion 93 that is provided on the ferrite core 91 in an overlapping manner. The ferrite core 91 and the diaphragm portion 93 are both ends open with a short-axis cylindrical case 94.
Has been inserted into.

The plane shape of the ferrite core 91 is shown in FIG. 6, and the vertical cross-sectional shape thereof is shown in FIG. Ferrite core 91
Is a partial disk-shaped bottom portion 91d cut along cutting lines c1 and c2 that are parallel to each other and have the same shortest distance from the center point k, and an arc wall shape that is erected in the axial direction from the upper surface of the peripheral portion of the bottom portion 91d. Pair of outer wall portions 91b composed of partial cylindrical walls of
And a central pillar portion 91a having a small diameter which is erected from the upper surface of the central portion of the bottom portion 91d in the axial direction. The space inside the outer wall portions 91b outside the central pillar portion 91a is the recess 90. . A resin bobbin 92a around which a coil 92 is wound is fitted on the central column portion 91a. A communication hole 91c that communicates the recess 90 with the outside (here, inside the tire) is formed in the outer wall portion 91b of the ferrite core 91 surrounding the recess 90 and the case 94.

The diaphragm portion 93 includes a thick disk-shaped base 93a, a short-axis cylindrical ring 93b, a thin disk-shaped diaphragm 93c, and a thin magnetic foil attached to the lower surface of the diaphragm 93c (the present invention). Magnetic film referred to in 9)
It consists of 3d. The base 93a has a ring-shaped protrusion 93e downward from the lower surface of the outer peripheral portion, while the diaphragm 93
In c, a peripheral wall is formed upward from the outer peripheral edge of the flat disk portion. The peripheral wall of the diaphragm 93c is fitted into the ring-shaped projection 93e of the base 93a and then welded to form a closed space S inside.

Therefore, the central portion of the lower surface of the magnetic foil 93d is close to the upper end surface of the central column portion 91a of the ferrite core 91 via the gap d, and the peripheral portion of the magnetic foil 93d is the outer wall portion of the ferrite core 91. It is in contact with the upper end surface of 91b. The ring 93b is fitted to the diaphragm 93c, the upper end surface of the ring 93b abuts the lower surface of the base 93a, and the lower end surface of the ring 93b and the upper end surface of the outer wall portion 91b of the ferrite core 91 sandwich the peripheral portion of the magnetic foil 93d. is doing. Therefore, this ring 93b is
1 defines the length of the gap d between the upper end surface of the central pillar portion 91a and the lower end surface of the magnetic foil 93d.
The length of the gap d can be changed by exchanging.

The magnetic foil 93d is made of an amorphous magnetic film having a thickness of about 0.03 mm, and has a plane shape equal to the horizontally projected shape of the ferrite core 91, as shown in FIG. That is, the magnetic foil 93d has a shape obtained by cutting a circular amorphous magnetic film by two cutting lines c3 and c4 which are parallel to each other and have the same shortest distance from the center point C.
Fine slits 9 parallel to each other in the peripheral portion and the central portion
30, 931 and 932 are formed in parallel with the cutting lines c1 and c2. By the way, the width between the cutting lines c3 and c4 is 12
mm, and the pitch of the slits 930 and 931 is 50 μm.

Of course, the magnetic foil 93d may be a circular amorphous magnetic film, a so-called magnetic tape coated with iron oxide fine particles, pure iron, or a silicon steel plate. The magnetic foil 93d is attached, vapor deposited, CVD, PV
It can also be formed by various methods such as D and coating. However, it is preferable to use a soft magnetic high magnetic permeability material having a small residual magnetization and a small magnetostriction coefficient. Base 93a, ring 9
Although 3b and the diaphragm 93c are made of stainless steel, any non-magnetic material may be used.

The diaphragm 93c itself can also serve as a magnetic film, in which case the magnetic foil 93d need not be attached. Further, in FIG. 8, the magnetic foil 93d is formed in a partial disk shape, but the shape is free. Further, the ferrite core 91 may be omitted. Now, when the tire air pressure changes, the differential pressure between the gas pressure filled in the closed space S and the tire air pressure changes, and this differential pressure change causes the diaphragm 93c to move vertically in FIG. The length of changes. As a result, the inductance L of the coil 92 changes. This change in the inductance L is simply output as an AC electrical signal by supplying an AC current to the coil 92. That is, when an alternating current is supplied to the coil 92, the ferrite core 91 and the magnetic foil 93d are
A magnetic flux is formed in the gapped magnetic circuit consisting of and, and this magnetic flux flows in the longitudinal direction in the magnetic foil 93d as shown in FIG.

However, the magnetic flux enters and leaves the magnetic foil 93d at a right angle to the magnetic foil 93d from the upper end surface of the outer wall portion 91b of the ferrite core 91. Similarly, the magnetic flux is the ferrite core 91
From the upper end surface of the central pillar portion 91a to the magnetic foil 93d.
Enter and exit at a right angle to 3d. Therefore, a large eddy current is generated in the magnetic foil 93d near the outer wall 91b and the central column 91a, as shown in FIG.

This eddy current becomes a resistance component which is connected in parallel with the inductance component of the coil 92 in the electric circuit. When the coil resistance and the hysteresis loss are neglected, the impedance of the coil as a whole is:
The inductance component and the resistance component due to the eddy current are equal to the impedance of the parallel connection circuit. Therefore, even if the inductance component of the coil 92 changes due to the displacement of the diaphragm 93c, the impedance change of the coil as a whole becomes small, the change rate of the current flowing through the coil becomes small, and the detection sensitivity deteriorates.

In this embodiment, in order to solve this problem, the magnetic foil 93d is provided with slits 930 and 931 so that the magnetic flux from the ferrite core 91 is generated by the magnetic flux.
A large eddy current when entering in the direction perpendicular to 3d is reduced. As a result, in this embodiment, the parallel resistance component of the impedance of the coil 92 is increased, and the detection sensitivity is significantly improved.

Furthermore, in this embodiment, when the magnetic foil 93d made of an amorphous alloy film having a small hysteresis loss (which also becomes a parallel resistance component with respect to the inductance component) is adopted, the eddy current loss is reduced. By effectively reducing, the parallel resistance component described above is largely eliminated and the detection sensitivity is improved. In addition,
It is convenient to reduce the power supply current because it can reduce the saturation of the magnetic foil 93d, the heat generation of the coil 92 and the ferrite core 91, and the power consumption.

It is preferable that the widths of the slits 930, 931 and 932 are small in order to prevent the saturation magnetic flux from decreasing. However, the position, shape and number of the slits in the magnetic foil 93d should be effective in reducing the eddy current. Of course, you are free to change. However, it is preferable that the slit direction is substantially equal to the magnetic flux flow direction when there is no slit, from the viewpoint of suppressing increase in magnetic resistance. In addition, the slits 930 and 93
1, 932 can be collectively formed at the time of stamping and forming the magnetic foil 93d.

FIG. 17 shows the measurement results of the relationship between the applied pressure and the inductance of the coil 92 by the pressure sensor having the same shape as the pressure section detecting section 9a, and FIG. 18 shows the result of the measurement by the pressure sensor having the same shape as the pressure section detecting section 9a. The measurement result of the relationship between the pressure and the displacement of the diaphragm 93c in the gap direction is shown. FIG. 11 shows a sectional view of the temperature detector 9b.

The temperature detecting portion 9b is a thin metal plate-shaped metal case.
Case 95, a cover plate 96 that seals the opening of the case 95 to form a closed space M inside the case 95, and an insulating film (not shown) is sandwiched between the cover plate 96 and fixed so as to be electrically insulated. And the piezoelectric capacitor 53. This piezoelectric capacitor 5
Reference numeral 3 is a barium titanate-based complex impedance element, but since the admittance component is predominant in the frequency band used in this embodiment, it is simply considered as a capacitor.

An equivalent circuit of the device of this embodiment is shown in FIG. Piezoelectric capacitor 53 and coil 9 of pressure / temperature detector 9
2 and the series capacitor 55 together with the rim-side coil 13 compose the resonance circuit 100 in the present invention. Specifically, the coil 92 and the series capacitor 55 that are connected in series to form an LC series circuit section are the rim. It is connected to both ends of the side coil 13, and further, piezoelectric capacitors 53 are connected to both ends of the rim side coil 13.

This resonance circuit 100 has two resonance frequencies f
1 and f2, and these f1 and f2 are defined by the following formulas 1 and 2. However, L ₁ is the inductance of the rim side coil 13, L ₂ is the inductance of the coil 92, and C ₁
Is the capacitance of the piezoelectric capacitor 53 for tire temperature detection,
C ₂ is the capacitance of the series capacitor 55.

[0035]

[Formula 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

[0036]

[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 these Equations 1 and 2, the two resonance frequencies f1 and f2 of the resonance circuit 100 are the impedances L ₁ and L ₂ , respectively. Since it is a function of C ₁ and C ₂ , if two impedances arbitrarily selected from these L ₁ , L ₂ , C ₁ and C ₂ are variables that change depending on tire state variables, the resonance frequency f 1, Detecting f2, Equation 1,
It can be seen that the above two variables of L ₁ , L ₂ , C ₁ and C ₂ can be calculated by solving 2. In this embodiment, as described above, C ₁ is a tire temperature variable and L ₂ is a tire pressure variable. Further, the tire temperature can be calculated from the obtained C ₁ and the tire pressure can be calculated from the L ₂ .

The excitation coil 99 is supplied with a variable frequency alternating current 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 is the resonance circuit 100.
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 (2) (see FIG. 13). Therefore, the excitation voltage V1 and the reception voltage V2
The frequency of the excitation voltage V1 may be adjusted so that the phase difference between and becomes π / 2, and the frequency value of the reception voltage V2 when the phase difference is π / 2 may be detected as the resonance frequency fr. In particular, when the resonance circuit 100 is in a resonance state, the reception voltage V2 of the reception coil 101 is maximum, so that the SN ratio of the reception voltage V2 is high and the detection accuracy thereof is improved. The excitation coil 9
The electromagnetic coupling between 9 and the receiving coil 101 is ignored here.

FIG. 14 shows an example of the ECU 35, and FIG.
The waveform of each part of ECU35 is shown in FIG. The voltage controlled oscillator (hereinafter, abbreviated as VCO) 206 is designed so as 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 limbed via the excitation coil 99. It is radiated to the side coil 13. As a result, the resonance circuit 100 is excited, and the electromagnetic wave emitted from the rim-side coil 13 causes an induced electromotive force V2 at both ends of the receiving coil 101. At this time, the waveform of the reception voltage V2 of the reception coil 101 becomes a sine wave. The waveform of the reception voltage V2 is the rectangular wave voltage V in phase with the reception voltage V2 by the comparator 201.
converted to k and VC in the exclusive OR gate 202
It is compared with the output voltage V1 of O206. As shown in FIG. 15, the output voltage Vg of the exclusive OR gate 202
Becomes a low level if the states of Vk and V1 are equal, and becomes a high level if they are different. Exclusive OR gate 202
Output voltage Vg is converted into a DC voltage Vf having a different level depending on the duty ratio by the low-pass filter 203, and the DC voltage Vf is compared with the reference voltage Vr from the reference voltage generator 204 in the control voltage generator 205. To be done.

The control voltage generator 205 outputs 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 that is uniquely determined by the value of the output voltage Vc. 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 becomes one half of the peak value Vgx of the output voltage Vg of the exclusive OR gate 202. Therefore, by setting the value of the reference voltage Vr output from the reference voltage generator 204 to be half the output voltage Vg of the exclusive OR gate 202, the oscillation frequency of the VCO 206 is always the resonance frequency of the resonance circuit.

Here, the microcomputer 209 determines the resonance frequency f1.
To detect the first voltage Vc to the control voltage generator 205.
1 and the control voltage generator 205 outputs the first voltage Vc1 to the voltage control oscillator 206 regardless of the voltages Vr and Vf by the built-in gate (not shown), and the voltage control oscillator 206 outputs the first voltage Vc1. It oscillates at a frequency according to the voltage Vc1.
The first voltage Vc1 is set in the vicinity of the first resonance frequency f1 of the resonance circuit 100, and as a result, the first voltage Vc1 is generated by the gate (not shown) incorporated in the control voltage generator 205.
If the output voltage Vc is output so that the output voltage of c1 is cut off and 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 sets the resonance frequency f2.
The second voltage Vc to the control voltage generator 205 when detecting
2, the control voltage generator 205 outputs the second voltage Vc2 to the voltage controlled oscillator 206 by the built-in gate (not shown) regardless of the voltages Vr and Vf, and the voltage controlled oscillator 206 outputs the second voltage Vc2. It oscillates at a frequency according to the voltage Vc2.
This second voltage Vc2 is set in the vicinity of the second resonance frequency f2 of the resonance circuit 100, and as a result, the control voltage generator 205 is supplied with a second voltage Vc by a gate (not shown) built therein.
When the output voltage Vc is output so that the output voltage of c2 is cut off and 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 above-mentioned first of the voltage controlled oscillator 206,
A process for obtaining the inductance L ₂ related to the tire pressure and the inductance C ₂ related to the tire temperature from the second resonance frequencies f1 and f2 will be described. The oscillation voltage V1 of the voltage controlled oscillator 206 is pulse-shaped by the Schmitt trigger 207, input to the counter 208 and counted, and the count value is appropriately sent to the microcomputer 209.

FIG. 16 shows the resonance frequency f of the microcomputer 209.
1 shows the f2 detection routine. First, the control voltage generator 2
The first voltage Vc1 is output to 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 outputs the first resonance frequency f
The microcomputer 209 waits for a 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 may be read, then the count value C2 may be read again with a certain time delay, and the difference C2-C1 may be calculated.

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

Next, the microcomputer 209 refers to the built-in map, calculates L ₂ and C ₁ based on the resonance frequencies f1 and f2 (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). (Modification) In FIG. 12, if the piezoelectric capacitor 53 is omitted, only the tire air pressure can be detected, and the circuit processing in that case is the same as that of the first embodiment, so the description thereof is omitted.

Even if the piezoelectric capacitor 53 is not placed in the closed space as shown in FIG. 11, it is possible to detect the temperature and the pressure from the resonance frequencies f1 and f2 by the equations 1 and 2. In this case, the electrostatic capacitance of the piezoelectric capacitor 53 changes with both pressure and temperature. 19 and 20 show another signal processing circuit of the pressure detector 9a. In FIG. 14, an AC power supply with a constant frequency (having a predetermined output impedance)
Power is supplied from 201 to the coil 92 and the capacitor C (constant) of the series resonance circuit through the coils 99 and 13. The oscillation frequency is selected near the resonance frequency of the series resonance circuit in advance. If the inductance of the coil 92 changes due to pressure change, the resonance frequency changes, and the input voltage to the detector 202 increases as the resonance frequency deviates from the oscillation frequency. To do.

Therefore, if the output voltage of the detector 54 is smoothed by the smoothing circuit 203, the output voltage becomes a function of the pressure change. In FIG. 20, the oscillation frequency of the variable oscillation circuit 301 is variable due to the series impedance of the inductance of the coil 92 and the capacitance of the capacitor C. Therefore, the oscillation voltage is converted to f / v by the f / v conversion circuit 302.
After conversion, if squared by the squaring circuit 303, the output voltage becomes a function of pressure change, and linearity is also improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of an essential part showing the overall configuration of a first embodiment of the present invention,

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

FIG. 3 is a schematic view showing a mounting state of the pressure detection unit of the first embodiment,

FIG. 4 is a plan view of FIG.

FIG. 5 is a cross-sectional view of the pressure detection unit inside the pressure temperature detection unit,

FIG. 6 is a plan view of a ferrite core in the pressure detection unit,

7 is a sectional view of the ferrite core of FIG. 6,

FIG. 8 is a plan view of the magnetic foil in the pressure detection unit,

FIG. 9 is a partial perspective view showing a flow of magnetic flux between a magnetic foil and a ferrite core in the pressure detection unit,

10 is a schematic perspective view showing a state of eddy current in the magnetic foil (when there is no slit) of FIG. 8,

FIG. 11 is a cross-sectional view of the temperature detection unit in the pressure temperature detection unit,

FIG. 12 is an equivalent circuit diagram of the first embodiment,

FIG. 13 is a graph showing the relationship between the output level and phase difference of the resonance circuit and the frequency;

FIG. 14 is a block circuit diagram of the ECU of the first embodiment,

FIG. 15 is a signal waveform diagram of each part of the ECU of FIG.

16 is a flow chart showing the tire pressure and temperature detection operation of the microcomputer in the ECU of FIG.

FIG. 17 is a characteristic diagram showing an actual measurement result of characteristics of a pressure sensor having the same shape as the pressure detection unit of FIG.

FIG. 18 is a characteristic diagram showing an actual measurement result of characteristics of a pressure sensor having the same shape as the pressure detection unit of FIG.

FIG. 19 is a block diagram showing another mode of a signal processing circuit system using the pressure detection unit of FIG.

20 is a block diagram showing another mode of a signal processing circuit system using the pressure detection unit of FIG. 5;

[Explanation of symbols]

 9a Pressure part detection part, 92 coil, 93c diaphragm 93d magnetic foil 94 case 930 slit 931 slit.

Claims (2)

[Claims] 1. A case, a diaphragm whose peripheral portion is supported by the case, and which is displaced according to a pressure difference of two fluids acting on both surfaces of a central portion, and a conversion portion which converts the displacement of the diaphragm into an electric signal. In the pressure sensor including, the conversion unit is disposed on the diaphragm and has a high magnetic permeability, and the displacement is performed by holding the case in close proximity to the magnetic film with a predetermined gap. The magnetic film includes a coil whose inductance changes according to the size of the gap, and a circuit section which supplies an alternating current to the coil to detect a signal component modulated by the inductance. A pressure sensor having a plurality of slits formed at predetermined intervals in parallel with the pressure sensor. 2. A magnetic circuit having a gap is formed together with the magnetic film so as to face each other in a predetermined region of the magnetic film via a minute gap, and the magnetic core has a coil wound around it. The pressure sensor according to claim 1, wherein the magnetic flux is formed in a region where the magnetic flux flows from the magnetic core.