JP3355971B2 - Piezoelectric conversion power supply and its piezoelectric transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric conversion type power supply suitable for use as a power supply for vehicles, earthquake alarms and the like, and a portable power supply.

[0002]

2. Description of the Related Art Conventionally, as a piezoelectric conversion type power supply of this type, there is a piezoelectric power generation apparatus as disclosed in Japanese Patent Application Laid-Open No. 7-107752. In this piezoelectric power generating device, as shown in FIG. 6, a piezoelectric conversion vibrator 3 in which a piezoelectric ceramic plate 1 is adhered to both surfaces of a phosphor bronze plate 2 is employed. The end 3a is fixed to the substrate 4 and extends from the substrate 4 in a cantilever manner.

By vibrating the piezoelectric conversion vibrator 3 with the fixed end 3a as a reference, the piezoelectric ceramic plates 1 are distorted, and an AC voltage is applied from these piezoelectric ceramic plates 1 in accordance with the piezoelectric conversion action. generate. Note that a cubic weight 5 is provided at the tip 3 b of the piezoelectric transducer 3, and the force F is intermittently applied to the weight 5 so that the piezoelectric transducer 3 vibrates smoothly.

[0004]

By the way, when the above-mentioned piezoelectric power generator is used as a power source of a tire pressure sensor of an automobile (see Japanese Patent Application Laid-Open No. 59-194677), the generated vibration of the automobile is 50 Hz to 200 Hz. Only peaks at frequencies in the range Therefore, even if the piezoelectric conversion vibrator 3 is supported in a cantilever shape as described above, the amount of charge generated per vibration of the piezoelectric conversion vibrator 3, that is, the amount of power generation is small. For this reason, there occurs a problem that it takes several tens of seconds to several minutes from when the vehicle starts running with a low tire pressure to when the warning is issued from the air pressure sensor.

[0005] Then, the cause of the low power generation of the piezoelectric ceramic plate 1 was examined. Generally, the piezoelectric transducer 3 is formed in a rectangular plate shape with a constant thickness as shown in FIG. Here, the thickness of the piezoelectric ceramic plate 1 is represented by t _P, and the substrate 4 and the weight 5
Let L and b _O be the distance and width between the two opposing walls, respectively.
In addition, assuming that a distance from a position of the piezoelectric ceramic plate 1 corresponding to the above-mentioned opposing wall of the substrate 4 (hereinafter, referred to as a fixed end) to a free end which is the tip 3b is x, a bending stress σ applied to the piezoelectric ceramic plate 1 Is represented by the following equation (1). The force F is applied to the weight 5.

[0006]

(Equation 1) Therefore, when the piezoelectric transducer 3 is vibrated as described above, the bending stress σ of the piezoelectric ceramic plate 1 becomes a maximum value σ _o when the piezoelectric transducer 3 is fixed as shown in FIG. It becomes smaller as it approaches the end 3b. Moreover,
The piezoelectric ceramic plate 1 generates a charge proportional to the bending stress σ.

Therefore, the electric charge of the piezoelectric ceramic plate 1 is
The free end 3b becomes maximum at the fixed end of the piezoelectric transducer 3
Decreases as it approaches. From this, it has been found that the amount of power generation of the piezoelectric ceramic plate 1 decreases as it approaches the free end 3b from the fixed end. On the other hand, the present inventor has noticed that the amount of power generation of the piezoelectric ceramic plate 1 can be increased by making the bending stress uniform and maximum over the entire piezoelectric ceramic plate 1. According to such an idea, at least one of the width b _O and the thickness t _P of the piezoelectric ceramic plate 1 is set so that the bending stress σ becomes a maximum value regardless of the distance x in the equation (1). I just need.

Accordingly, the present invention provides a piezoelectric conversion type power supply and a piezoelectric conversion vibrator in which the shape of the piezoelectric conversion vibrator is devised based on the above idea so that the maximum bending stress is uniformly applied to the whole. The purpose is to provide.

[0009]

According to the first to fourth aspects of the present invention, the thickness of the piezoelectric transducer is reduced from the fixed end to the free end.
A piezoelectric plate on the surface of a metal plate formed with a certain width
The thickness of the plate decreases from the fixed end to the free end.
It is characterized by being formed with a constant width. Thus, when the piezoelectric transducer vibrates, the entire area between the fixed end and the free end of the piezoelectric transducer vibrates uniformly at the fixed end, that is, the maximum bending stress. Therefore, the piezoelectric transducer vibrates uniformly to generate the maximum charge corresponding to the maximum bending stress over the entire region between the fixed end and the free end. As a result, the power generation efficiency of the piezoelectric transducer can be greatly improved.

[0010]

[0011]

[0012]

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIG.
4 through FIG. FIG. 1 shows an example in which a piezoelectric conversion type power supply according to the present invention is applied as a power supply for a sensor circuit S of a vehicle occupant protection system. This piezoelectric conversion type power supply includes a bimorph type plate-shaped piezoelectric conversion vibrator P.

The piezoelectric transducer P has a fixed end P
2, as shown in FIG. 2, the piezoelectric transducer P is fitted into a slit-shaped recess 11 a formed in an outer wall 11 of a stationary plate 10 constituting a part of the vehicle body of the vehicle.
Extends perpendicularly to the outer wall 11 from the fixed end P1.
However, the planar shape of the piezoelectric transducer P is an isosceles triangle.

As shown in FIGS. 2 and 3, the piezoelectric transducer P has a metal plate 20, both piezoelectric plates 30, 40 and both electrode plates 30a, 40a formed in the same isosceles triangle.
The two piezoelectric plates 30 and 40 are formed of a metal plate 2.
0 are attached to both surfaces by a conductive adhesive. As a result, the two piezoelectric plates 30 and 40 are
Are connected in series.

If it is desired to increase the electric charge more than the voltage, the piezoelectric plates 30 and 40 may be changed so that they are connected in parallel. Although the metal plate 20 is made of brass or the like, in a vehicle having a large temperature change, it is preferable to form the metal plate 20 with copearl having a small coefficient of thermal expansion. Piezoelectric transducer P
Is from the fixed end P1 to the tip P which is a free end.
The width gradually decreases toward 2.

The two piezoelectric plates 30 and 40 are both formed of the same piezoelectric material.
Due to the distortion in the thickness direction, a piezoelectric conversion effect is exhibited.
The two electrode plates 30a, 40a are attached to the outer surfaces of the two piezoelectric plates 30, 40, respectively, with a conductive adhesive.
The metal plate 20, the piezoelectric plates 30, 40, and the electrode plates 3
The plate thicknesses of the piezoelectric plates 30 (or 40) / the plate thickness of the metal plate 20 indicate that the piezoelectric plate 30 (or 40) has the maximum piezoelectric amount. About 35 is good.

A cubic weight 50 is fitted to the free end P2 of the piezoelectric transducer P as shown in FIG. 2, and this weight 50 is the same as the weight 5 in FIG. In addition,
The reason why the tip end of the piezoelectric transducer P is a free end and the weight 50 is provided at the free end is that the peak of the generated vibration of the vehicle is as low as 50 to 200 Hz, and the piezoelectric plate 30 This is for making the 40 resonate.

Here, the grounds for forming the planar shape of the piezoelectric transducer P in the form of an isosceles triangle with the same plate thickness as described above will be described. The thickness of each of the piezoelectric plates 30 and 40 is set to t _{P as} shown in FIG. 3 similarly to the thickness of the piezoelectric ceramic plate 1. The piezoelectric of the outer wall 11 (piezoelectric transducer vibrator corresponds to a substantial fixed end P ₁₁ of P of the fixed end portion P1) and the weight 50 against which the opposed walls (free end portion P2 of the stationary plate 10 the distance between the corresponding) and a substantial free end P ₂₁ conversion vibrator P, as in the case of the piezoelectric ceramic plate 1 and L.

Further, the fixed end P of the piezoelectric transducer P
₁₁ is the same as the width of the piezoelectric ceramic plate 1 b
And _O, and a distance towards the free end P ₂₁ from the fixed end P ₁₁ of the piezoelectric conversion vibrator P, and the x as in the case of the piezoelectric ceramic plate 1. The force F is applied to the weight 50. Under such a premise, the bending stress σ to be applied to each of the piezoelectric plates 30 and 40 at the distance x = L,
That is, the maximum bending stress σ _O applied to the piezoelectric plate is expressed by the following equation 2 based on the above equation 1. The maximum bending stress σ _O is a value that takes into account the safety factor of the fixed end of the piezoelectric transducer P.

[0021]

(Equation 2) Here, in order to apply the maximum bending stress σ _O to each of the piezoelectric plates 30 and 40 irrespective of the distance (L−x) under a constant plate thickness t _P , the distance between the piezoelectric transducers P and Assuming that the width at x is b, the following equation (3) may be satisfied.

[0022]

(Equation 3) From the equation (3), the following equation (4) representing the width b is obtained.

[0023]

(Equation 4) According to this, the width b is the distance from the fixed end P ₂₁ (L-x)
Is proportional to the bending stress σ of the piezoelectric transducer P
It can be seen that the maximum bending stress σ _O is obtained in all regions of the piezoelectric transducer P between the fixed end P ₁₁ and the free end P ₂₁ . This generated charge amount of each of the piezoelectric plates 30 and 40, to be a maximum charge amount in all areas between the fixed end P ₁₁ of each of the piezoelectric plates 30 and 40 and free end P ₂₁ (See FIG. 4).

Therefore, the planar shape of the piezoelectric transducer P is an isosceles triangle as described above. By the way, the piezoelectric plate 3
The generated charge amount Q ₃₀ 0, I tried to calculate the generated charge amount to Q ₁ piezoelectric ceramic plate 1 in FIG. Assuming now that the generated charge amount is generally Q, the generated charge amount Q is expressed by the following equation 5 based on the bending stress σ.

[0025]

Where A is a constant, which is substantially equal to the plate thickness t _P. D is a piezoelectric constant. Therefore, the generated charge amount Q ₁ is calculated by using σ according to the equation (1) and the equation (5).
It can be expressed by the following equation (6).

[0026]

(Equation 6)

The generated charge amount Q ₃₀ is expressed by the following equation (7) based on the equation (5), where σ = maximum bending stress σ _O (see equation (3)).

[0028]

(Equation 7) However, in both the piezoelectric ceramic plate 1 and the piezoelectric plate 30, the constants A and d in Equation 5 are the same.

Thus, based on both equations (6) and (7),
The following equation (8) is obtained.

[0030]

(Equation 8) According to the equation (8), it can be seen that the amount of charge generated on the piezoelectric plate 30 is twice the amount of charge generated on the piezoelectric ceramic plate 1.

Therefore, if the surface area of the piezoelectric transducer P is half the surface area of the piezoelectric transducer 3, the capacitance of the piezoelectric transducer P is half the capacitance of the piezoelectric transducer 3. . Therefore, using the result of the equation (8), it can be seen that the amount of electric charge generated on the piezoelectric plate 30 is the same as the amount of electric charge generated on the piezoelectric ceramic plate 1. This means that the voltage generated by the piezoelectric plate 30 is twice as large as the voltage generated by the piezoelectric ceramic plate 1 from Q = CV. Therefore, the piezoelectric plate 3
The power generation amount {(1/2) QV} of 0 is also twice that of the piezoelectric ceramic plate 1. Note that when Q = CV, C and V
Are the capacitance and the generated voltage, respectively.

The piezoelectric conversion type power supply includes a full-wave rectifier 60 connected to the piezoelectric conversion vibrator P, a capacitor 70 connected to the full-wave rectifier 60, and a load adjusting variable resistor 80.
And The full-wave rectifier 60 includes a piezoelectric transducer P
Full-wave rectification of the generated voltage. The capacitor 70 is charged by the full-wave rectified output of the full-wave rectifier 60. The load adjusting variable resistor 80 is connected in parallel with the capacitor 70 and the sensor circuit S, and the variable resistor 80 is adjusted so as to increase the power generation output efficiency from the piezoelectric transducer P.

In the above-described embodiment, when the piezoelectric transducer P is vibrated by the force F, the piezoelectric plates 30 and 40 vibrate in the thickness direction with the fixed end P1 as a reference.
Generates electric charge. Here, as described above, the piezoelectric conversion vibrator P is formed in an isosceles triangular shape. Therefore, the entire region between the fixed end P ₁₁ of the piezoelectric plate 30 and 40 with the free end P ₂₁ is bending stress in the fixed end P _11, i.e., to vibrate uniformly subjected to the maximum bending stress of the piezoelectric plate. Therefore, the piezoelectric plate 3
The entire area between the fixed end P ₁₁ of 0,40 free end P ₂₁ generates the maximum amount of charge corresponding to uniformly the maximum bending stress.

As a result, the power generation efficiency of the piezoelectric transducer P can be greatly improved. Further, when the piezoelectric transducer vibrator P generates an AC voltage in accordance with the generated charge, the full-wave rectifier 60 performs full-wave rectification on the AC voltage, and the capacitor 70 receives the AC voltage and is charged. Then, the sensor circuit S operates by receiving the charging voltage of the capacitor 70.

In this case, as described above, since the amount of charges generated by the piezoelectric transducer P is large, the charging voltage and charging power of the capacitor 70 can be sufficiently ensured. Therefore, the sensor circuit S
Can demonstrate its original function in a timely manner. In addition,
Since the piezoelectric conversion vibrator P has a compact shape, the piezoelectric conversion type power supply can be provided as a small power supply with a large amount of power generation.

Next, a modification of the above embodiment will be described with reference to FIG. In this modification, the bimorph type piezoelectric plate conversion vibrator Pa is at its fixed end P _{a 1,} instead of the piezoelectric conversion vibrator P described in the above embodiment, the stationary plate 10
Is fitted in a recess formed in place of the recess 11a, and the piezoelectric transducer Pa extends from the fixed end _Pa1 at right angles to the outer wall 11. However, the planar shape of the piezoelectric transducer vibrator P is rectangular, like the planar shape of the piezoelectric ceramic plate 1.

The piezoelectric transducer Vi includes a metal plate 80, both piezoelectric plates 90 and 100, and both electrode plates 90a and 100a, both of which are formed in the same rectangular shape. As shown by 5, each of the metal plates 80 is adhered to both surfaces by a conductive adhesive.
Here, the width of the piezoelectric transducer Pa is the same as the width b _O of the piezoelectric ceramic plate 1. Further, the plate thickness of the piezoelectric transducer Vi is from the fixed end P _a1 to the tip P which is a free end.
_It gradually becomes thinner _{toward a2} .

As described above, the width b _O of the piezoelectric transducer Pa is obtained.
The reason why the thickness of the piezoelectric transducer Pa is changed as described above is that the piezoelectric transducer P described in the above embodiment is used.
This is because the maximum bending stress at the position corresponding to the outer wall 11 of the stationary plate 10 of the piezoelectric conversion vibrator Pa is applied to the entirety of the piezoelectric conversion vibrator Pa in the same manner as in the case where is isosceles triangular.

For this reason, the metal plate 80 is formed of the same material as the metal plate 20 so that the thickness gradually decreases from the fixed end P _a1 to the tip P _a2 . Both piezoelectric plates 90, 1
00 is made of the same piezoelectric material as the two piezoelectric plates 30 and 40. Each of the piezoelectric plates 90 and 100 exerts a piezoelectric conversion action due to distortion in the thickness direction.

The two electrode plates 90a and 100a are
It is attached to the outer surfaces of 0 and 100, respectively. The two piezoelectric plates 90, 100 and the two electrode plates 90a, 100
Each plate thickness of a is constant. Further, the free end P _a1 of the piezoelectric conversion vibrator Pa is the weight 50 described in the above embodiment is fitted. Other configurations are the same as those of the above embodiment.

In the present modified example, when the piezoelectric transducer Pa is vibrated by the force F, the piezoelectric plate 9
0 and 100 vibrate in the plate thickness direction based on the fixed end P _a1 ,
Generates electric charge. Here, as described above, the piezoelectric transducer Pa is formed so that the plate thickness is reduced from the fixed end to the free end. Therefore, the piezoelectric transducer Pa
The entire area between the fixed end P _a11 (corresponding to the fixed end P ₁₁ ) and the free end P _a21 vibrates while uniformly receiving the bending stress σ at the fixed end P _a11 , that is, the maximum bending stress σ _O. . Therefore, the entire area between the fixed ends and the free ends of the piezoelectric plates 90 and 100 uniformly generates the maximum charge amount corresponding to the maximum bending stress.

As a result, it is possible to greatly improve the power generation efficiency of the piezoelectric transducer Pa while securing the functions and effects described in the above embodiment. The shape of the piezoelectric transducer Pa is not limited to the shape described in the present modification, but may be a trapezoid. In implementing the present invention, the piezoelectric transducer P,
The present invention is not limited to the case where the planar shape or the plate thickness shape is changed as in Pa, but may be generally implemented by forming the plate-shaped piezoelectric transducer in a uniform beam shape. Here, the uniform beam means that the shape of the piezoelectric transducer is formed such that the bending stress applied over the entire region between the fixed end and the free end of the piezoelectric transducer is substantially uniform. .

In the embodiment of the present invention, the piezoelectric plates and the electrode plates of the piezoelectric transducers P and Pa are provided to prevent waste.
It may be implemented short so as not to enter the inside of the stationary plate 10 and the weight 50. Further, in the embodiment of the present invention, the present invention is not limited to the bimorph-type piezoelectric transducers P and Pa, but may be applied to a unimorph-type pressure plate-like transducer (a piezoelectric plate and an electrode plate attached to one surface of a metal plate). You may apply and implement this invention.

Specifically, the planar shape of the unimorph type plate-shaped piezoelectric transducer is made to be an isosceles triangle, or the thickness of the piezoelectric transducer is changed in the same manner as the thickness of the piezoelectric transducer Pa. Even in this case, the same operation and effect as described in the above embodiment and modified examples can be achieved. The full-wave rectifier 6
Instead of 0, a half-wave rectifier rectifies the piezoelectric voltage of the unimorph plate-shaped piezoelectric transducer.

Further, in the above embodiment, an example was described in which the planar shape of the piezoelectric transducer P was an isosceles triangle. However, the present invention is not limited to this.
It may be implemented as a triangular shape such as a right triangle. Further, in the embodiment of the present invention, the shape of the piezoelectric transducer is not limited to the shape described in the above embodiment or the modified example, and may be bent over the entire region between the fixed end and the free end of the piezoelectric transducer. If the stress is applied uniformly, the shape of the piezoelectric transducer may be, for example, a trapezoidal shape.

Further, in practicing the present invention, the present invention is not limited to a sensor circuit of a vehicle occupant protection system, but is applied to a power source of various moving bodies such as ships, industrial equipment, earthquake alarms, position alarms, and the like. You may apply and implement.

[Brief description of the drawings]

FIG. 1 is a schematic overall configuration diagram showing an embodiment of the present invention.

FIG. 2 is a perspective view showing a state where the piezoelectric transducer of FIG. 1 is attached to a stationary plate.

FIG. 3 is an enlarged perspective view of the piezoelectric transducer shown in FIG. 2;

4 is a graph showing that a bending stress in a region from a fixed end to a free end of the piezoelectric transducer of FIG. 2 is constant at a maximum value σ _O.

FIG. 5 is a side view showing a modification of the embodiment.

FIG. 6 is a perspective view showing an attached state of a conventional piezoelectric transducer.

7 is a graph showing a tendency that bending stress in a region from a fixed end to a free end of the piezoelectric transducer of FIG. 6 decreases from a maximum value σ _O.

[Explanation of symbols]

P, Pa ... piezoelectric conversion vibrator, P ₁₁ ... fixed end, P ₂₁ ... free end, 10 ... stationary plate, 50 ... weight, 60 ... full-wave rectifier, 7
0: Capacitor.

──────────────────────────────────────────────────続 き Continued from the front page (72) Inventor Mamoru Ishikiriyama 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (56) References JP-A-9-205781 (JP, A) JP-A-10- 56784 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02N 2/00 H01L 41/09

Claims (4)

(57) [Claims] 1. A fixed end (P) fixed to a stationary member (10).
₁₁ , P _a11 ) and extend at the free end (P ₂₂ ,
P _a22 ), a bimorph plate-shaped piezoelectric transducer (P, Pa), which generates a piezoelectric output in response to vibration in the thickness direction with respect to the fixed end, A weight (50) provided at the free end of the piezoelectric transducer for promoting the vibration of the piezoelectric transducer, and a rectifier (6) for rectifying the piezoelectric output of the piezoelectric transducer.
0), and a smoothing means (70) for smoothing the rectified output of the rectifying means to a DC output, wherein the piezoelectric transducer is connected from the fixed end to the free end.
Metal formed with a constant width to reduce the thickness
Plate and a piezoelectric plate attached to each side of this metal plate
Having a plate thickness from the fixed end to the free end.
A piezoelectric conversion type power supply characterized by being formed with a constant width so as to be thin . 2. A fixed end (P) fixed to a stationary member (10).
₁₁ , P _a11 ) and extend at the free end (P ₂₂ ,
P _a22 ), which is a unimorph plate-shaped piezoelectric transducer (P, Pa), which generates a piezoelectric output in response to vibration in the thickness direction with respect to the fixed end, A weight (50) provided at the free end of the piezoelectric transducer for promoting the vibration of the piezoelectric transducer, and a rectifier (6) for rectifying the piezoelectric output of the piezoelectric transducer.
0), and a smoothing means (70) for smoothing the rectified output of the rectifying means to a DC output, wherein the piezoelectric transducer is connected from the fixed end to the free end.
Metal formed with a constant width to reduce the thickness
Plate and a piezoelectric plate affixed to one side surface of this metal plate
Having a thin plate thickness from the fixed end to the free end.
A piezoelectric power supply characterized by being formed with a constant width . 3. A stationary member (10) having a fixed end (P ₁₁ , P
The free end at extending out the distal end is fixed at _a11) a (P ₂₂₎
Bimorph type plate-shaped piezoelectric transducers (P , Pa) to be formed
And responds to vibration in the thickness direction with respect to the fixed end.
Piezo-electric conversion vibration for a piezo-electric conversion type power supply that generates piezoelectric output
A thickness of the plate is reduced from the fixed end to the free end.
Metal plate formed with a fixed width on both sides of this metal plate
And a piezoelectric plate attached to each of the fixed ends.
From the free end to the free end
For piezoelectric conversion type power supply characterized by being formed by
Piezoelectric transducer. 4. A fixed end (P ₁₁ , P ₁₁ )
The free end is fixed by extending out the distal end by _a11) (P _22, P
_a22 ) Unimorph-type plate-shaped piezoelectric transducer that forms
(P, Pa) in the thickness direction with respect to the fixed end
For piezoelectric conversion type power supply that generates piezoelectric output in response to vibration
In the piezoelectric transducer , the plate thickness is reduced from the fixed end to the free end.
A metal plate formed at a constant width on one side of this metal plate
And a piezoelectric plate attached to the surface, from the fixed end
At a constant width so that the plate thickness becomes thinner toward the free end
Piezoelectric conversion type power supply characterized by being formed
Transducer.