JPH0614062B2 - Flow velocity detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a flow velocity detecting device using an element. Since the flow velocity detecting device of the present invention is small in size, excellent in durability, quick response, and high in precision, it can be mounted on a fluid such as an automobile and used for detecting wind velocity.

[Conventional technology]

Conventionally, a flow velocity detection device that detects a flow velocity using a piezoelectric element is known.

[Problems to be solved by the invention]

However, since the flow velocity detection device using the conventional piezoelectric element detects the flow velocity based on the magnitude of the voltage applied to the piezoelectric element and the magnitude of the current supplied to the piezoelectric element,
There is a problem that the error of the detected flow velocity is large due to the fluctuation of the applied voltage.

In particular, this problem is important in a vehicle flow velocity detection device that is powered by an on-vehicle battery or an alternator. Of course, it is possible to add it to the constant voltage power supply device, but it is inevitable that the device configuration becomes complicated and power consumption increases.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a flow velocity detection device having a small detection error regardless of fluctuations in applied voltage.

[Means for solving problems]

The flow velocity detecting device of the present invention includes an element 1 that generates strain according to an applied electric field and generates electric polarization according to stress, and a mechanical force transmission means that is coupled to the element 1 and that transmits fluid pressure to the element. 2, a drive unit 3 for applying an AC electric field to the element, a detection for detecting a phase difference between a voltage applied to the element and a current flowing through the element, and a detection for detecting a flow velocity of the fluid according to the phase difference. It is characterized by comprising a part 4 and

The element 1 converts the pressure exerted by the fluid on the mechanical force transmitting means 2 into electric polarization, and also converts the electrical energy applied by the drive unit 3 into mechanical energy to vibrate the mechanical force transmitting means 2. The element 1 includes barium titanate (BaTiO ₃ ), lead titanate (PbTiO ₃ ), lead zirconate (PbZrO ₃ ), lead zircon titanate (PbZrO ₃ ).
Intrinsic ceramics such as b (Ti, Zr) O ₃ ) and modified ceramics obtained by adding additives to these can be used. The element 1 may be used alone, or a plurality of elements may be used at the same time. The shape of the element 1 may be any shape as long as it can fulfill the above function.

The mechanical force transmission means 2 transmits the pressure resulting from the flow velocity of the fluid to the element 1. The mechanical force transmission means 2 may be constituted by a separate member that is in close contact with the element 1 integrally,
Alternatively, the element 1 may be used as it is as the mechanical force transmission means 2.

The drive unit 3 applies an AC electric field to the element 1 to generate strain in the piezoelectric element 1. The drive unit 3 is composed of at least a drive source 30 and an electrode 31 integrally formed with the element 1 on the end face of the element 1.

The detection unit 4 detects the phase difference between the element applied voltage and the element conduction current as a physical quantity related to the flow velocity, and detects the flow velocity according to the phase difference.

[Action]

In FIG. 1, the element 1 is applied with an AC electric field by the drive unit 3 to generate strain. Since the applied electric field is an alternating electric field, the strain fluctuates periodically, and thus the element 1 vibrates. The vibration is transmitted to the mechanical force transmission means 2 and amplified. The detector 4 detects the voltage applied to the element 1 and the current flowing through the element 1, and detects the phase difference from them. This phase difference is a physical quantity that is affected by the strain amount of the element 1. Now, when the fluid flows at a flow velocity u and a pressure is applied to the mechanical force transmitting means 2, the mechanical force transmitting means 2 is displaced according to the pressure. The element 1 is distorted in response to the displacement, and this appears as a change in the phase difference between the voltage and the current. The change detection unit 4
Is detected, and the flow velocity is detected based on this.

〔Example〕

 Hereinafter, the present invention will be described in detail based on specific examples.

(1) First Embodiment FIG. 4 is a block diagram of the flow velocity detecting device of the present embodiment.
The figure is an attachment diagram of the sensor portion (portion constituted by the piezoelectric element 1 and the mechanical force transmitting means 2) of the flow velocity detecting device to the frame 71, and FIG. 3 is the flow velocity detecting device S ₀ of this embodiment. FIG. 6 is a view showing how the flow path R ₀ is attached.

As shown in FIG. 4 and FIG. 2, in this embodiment, the sensor unit includes two piezoelectric elements 11 and 12 (a plate-like rectangular parallelepiped shape, lead zircon titanate (trade name: PZT porcelain), and the two piezoelectric elements. The mechanical force transmitting means 2 (a plate-shaped rectangular parallelepiped longer than the piezoelectric element, made of Kovar) is sandwiched between the elements 11 and 12, and one end 21 projects from the two piezoelectric elements.

The first electrode 311 and the second electrode 311 are provided on each end surface of the first piezoelectric element 11.
The electrodes 312 are respectively formed by vapor deposition of silver (Ag), and the third electrodes 313,
The fourth electrodes 314 are similarly formed.
The electrodes may be made of a metal other than silver and may be formed by printing or plating. The second electrode 312, the third electrode 313 and the mechanical force transmission means 2 can be fixed to each other by using an adhesive or by soldering. Two
The polarization directions of the two piezoelectric elements 11 and 12 when there is no electric field are the same, which is the direction of arrow P in the figure. The piezoelectric elements 11, 1
2 and the mechanical force transmission means 2 need to have similar thermal expansion coefficients.

As shown in FIG. 2, the sensor portion having such a configuration is fixed to the frame body 71 via the upper and lower support plates 61 and 62 and the screw 72. Further, the piezoelectric elements 11, 1 of the mechanical force transmission means 2
2 portion projecting from (diaphragm 21) via the sealing member R _1, protrudes out of the frame 71, the channel R ₀ as shown in FIG. 3
Has been inserted into. The vibrating plate 21 and the fluid flow direction are perpendicular to each other. The other end of the mechanical force transmission means 2 (the diaphragm 2
The lead wire 310 is connected to the end portion on the side which is not 1.
The lead wire 310 is connected to an AC power source which is the driving source 30. Lead wires 3101 and 3102 are connected to the support plates 61 and 62, respectively.
01 and 3102 are connected to the detection unit 4.

As shown in FIG. 4, in this embodiment, the detection unit 4 is composed of a current detector 41, a voltage detector 42, and a phase difference calculation means 40 connected to these.

The flow velocity detecting device of this embodiment functions as follows.

When an AC electric field is applied to the first piezoelectric element 11 and the second piezoelectric element 12 by the AC power supply 30, the piezoelectric elements 11 and 12 are respectively distorted according to the AC electric field. For example, the second electrode 31
2, the third electrode 313 side to a negative potential, and the first electrode 31
When the first and fourth electrodes 314 are kept at a positive potential, the first piezoelectric element 11 expands and the second piezoelectric element 12 contracts. As a result, the diaphragm 21 bends downward in the drawing like 21b. On the contrary, the side of the second electrode 312 and the third electrode 313 is set to a positive potential, and the first electrode 3
If the 11th fourth electrode 314 side is kept at a negative potential, the first piezoelectric element 11 contracts and the second piezoelectric element 12 expands. As a result, the diaphragm 21 bends upward in the figure. Since the electric field being applied is an alternating electric field, the vibration plate 2 is repeated by repeating the above operation.
1 vibrates.

In such a state, the fluid flows at a flow velocity u, and when pressure is applied to the diaphragm 21, the pressure is transmitted to the piezoelectric elements 11 and 12 by the mechanical force transmitting means 2.

Therefore, a direct current strain corresponding to the flow velocity is generated in the piezoelectric elements 11 and 12, the strain is generated in each of the piezoelectric elements 11 and 12, and a polarization based on the strain is generated in each of the piezoelectric elements 11 and 12. Due to the polarization, the phase of the current flowing through the piezoelectric elements 11 and 12 changes with respect to the applied voltage.

5 and 6 are graphs showing the phase difference between voltage and current. FIG. 7 is a graph showing the relationship between the flow velocity value u and the phase difference θ.

The phase difference between the applied voltage curve A and the current curve B when the flow velocity is zero is θ ₀ as shown in FIG. Next, when the fluid flows at the flow velocity u, strain is generated in the piezoelectric elements 11 and 12, and this appears as a change in current. FIG. 6 is a diagram showing the relationship between the voltage curve A and the current curve B when the flow velocity is u. That is, the phase difference between the two curves when the flow velocity is u is θu. Here, the relationship between the phase difference between the voltage curve A and the current curve B and the flow velocity is represented by the curve shown in FIG. Therefore, when the phase difference calculation unit 40 detects the phase difference, the flow velocity can be calculated.

(Application Example) An application example of the flow velocity detecting device of the present invention will be described below.

FIG. 8 is a perspective view showing a state in which the flow velocity detecting device of the present invention is mounted on the roof of an automobile, FIG. 9 is a configuration diagram showing the details of the flow velocity detecting device to be mounted, and FIG. It is a top view of a figure. Further, FIG. 1 is a block diagram in which the wind direction and wind speed are calculated from the flow velocity detecting device shown in FIG. 9 and output to the actuator.

As shown in FIG. 9, in this application example, the flow velocity detecting device is 2
It has two sensor sections Sa and Sb. Two sensor parts S
The vibrating plates 2a and 2b of a and Sb are respectively arranged in separate flow paths Ra and Rb at right angles to the flow direction. The two flow paths Ra and Rb are orthogonal to each other as shown in FIG. 10, and with respect to the direction of the fluid inlet (flow direction),
Each makes an angle of 45 degrees. Therefore, if the air is U in the figure
When the air flows in from the direction a, the velocity of the air flow flowing in the flow channel Ra is faster than the velocity of the air flow flowing in the flow channel Rb, and conversely, when the air flows in from the direction Ub, the velocity of the air flow flowing in the flow channel Rb flows. It is faster than the velocity of the air flow flowing through the passage Ra. Further, as shown in the figure, when air flows in from the direction of U ₀ , the velocities of the air flows flowing through the channels Ra and Rb are equal. Therefore, the wind direction can be obtained by calculating the velocities of the air flows in the flow channels Ra and Rb. Further, as shown in FIG. 11, by taking into consideration the signal from the vehicle speed sensor SS, not only the relative wind direction wind speed but also the absolute wind direction wind speed can be calculated and displayed. The relative or absolute wind direction and wind speed calculated in this way can be output to the actuator 9 to make the vehicle control more stable.

(Modification) In each of the above-described embodiments and application examples, two sensor units are used.
Although one composed of one piezoelectric element and one mechanical force transmitting means sandwiched between the two piezoelectric elements is used, this does not necessarily mean the above limitation.

FIG. 12 is a diagram showing a modification of the sensor unit. That is, as shown in FIG. 12 (A), the sensor portion may be composed of one piezoelectric element 1 and one mechanical force transmitting means 2 in close contact with the piezoelectric element, or as shown in FIG. 12 (B). The sensor portion may be composed of one piezoelectric element 1 and two mechanical force transmitting means 21 and 22 which are closely attached to both end surfaces of the one piezoelectric element 1, respectively, and as shown in FIG. 1
It is also possible to increase the length of the piezoelectric element and to bond two of them to use the piezoelectric element itself as the mechanical force transmitting means 2.

Further, as shown in (D), the structure of the sensor unit may be substantially the same as that of the above-described embodiment and application example, and the mechanical force transmission means 2 may be made of resin. In this case, the lead wires 3105, 310
6 is connected to the second electrode and the third electrode.

FIG. 13 is a diagram showing another modification of the shapes of the mechanical force transmitting means 2 and the piezoelectric element 1. That is, in each of the embodiments and application examples described above, the piezoelectric element 1 and the mechanical force transmitting means 2 are both plate-shaped rectangular parallelepipeds, but this is not limited to a rectangular parallelepiped.
A triangular shape as shown in (A), or (C),
A circular shape may be used as shown in (D). Frequency 2
In each of the above-described embodiments and application examples, the forming portion of No. 1 is projected from one end of the piezoelectric element (the right end in each drawing), but this does not necessarily have to be projected from one end.
As shown in (B), the diaphragm 21 may be formed in the middle of each piezoelectric element 1. The same applies to (D) or (C).

FIG. 14 is a diagram showing the positional relationship between the flow direction of the fluid and the diaphragm 21.

In all of the above embodiments, the diaphragm 21 is arranged at right angles to the fluid flow direction, but this is not a limitation. That is, as shown in FIG. 14 (A), they may be arranged to face each other in the flow direction, or as shown in FIG. 14 (B), they may be arranged at an angle of 45 degrees. Further, as shown in (C), it may be 135 degrees, and as shown in (D), it may be in the flow direction. Further, as shown in (E), the direction of flow and the direction of twist may be used. The point is that the diaphragm 21 may be arranged so as to receive some pressure due to the flow of fluid.

In the above examples, the piezoelectric element was used as the element, but it may be an electrostrictive element.

〔The invention's effect〕

In short, the present invention is a flow velocity detection device configured by using a piezoelectric element.

Since the flow velocity detecting device of the present invention uses the piezoelectric element, the entire shape can be reduced in size. Further, since the flow velocity is detected by the piezoelectric change, the responsiveness is good and the accuracy is high. Further, it is suitable to use atmosphere resistance against water, dust, dust and the like. Further, since the flow velocity is detected as an electric signal, it is convenient when the signal is used for controlling the actuator in the next stage. Also, the structure is relatively simple and the durability is good.

Furthermore, in the present invention, since the flow velocity is detected based on the phase difference between the applied voltage and the energizing current of the piezoelectric element that generates strain according to the flow velocity, it is simply based on the applied voltage or the energizing current. The flow velocity detection accuracy can be significantly improved as compared with the case of performing the flow velocity detection.

That is, as is well known, the phase difference corresponds to the time difference between the applied voltage and the energized current, and the energized current fluctuates according to the fluctuation of the applied voltage, but the phase difference does not change regardless of the fluctuation of the applied voltage. , It has the advantage that the detected flow velocity value does not fluctuate due to fluctuations in the applied voltage. And, of course, the above effect is particularly effective in the vehicle flow velocity detection device in which the fluctuation of the power supply voltage is large.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of the present invention. FIG. 2 is an attachment diagram of the sensor part of the flow velocity detecting device of the present embodiment to the frame, FIG. 3 is an attachment diagram of the flow velocity detecting device to the flow path, and FIG. 4 is of the present embodiment. It is a block diagram of a flow velocity detection device, FIGS. 5 and 6 are graphs showing the phase shift between the voltage curve and the current curve, and FIG. 7 is a graph showing the relationship between the flow velocity and the phase difference. FIG. 8 is a perspective view showing a state in which the flow velocity detecting device of the present invention is mounted on an automobile, FIG. 9 is a perspective view showing details of a sensor portion of the flow velocity detecting device in FIG. 8, and FIG. It is a top view of FIG. The first
FIG. 1 is a block diagram of a circuit in which the flow velocity detecting device shown in FIGS. 9 and 10 is mounted on the vehicle shown in FIG. 8 to calculate relative and absolute wind speeds and output to an actuator. 12 (A), (B), (C), and (D) are schematic sectional views showing modified examples of the sensor unit of the flow velocity detecting device.
13 (A), (B), (C), and (D) are a cross-sectional view and a plan view showing a modified example of the arrangement of the element of the sensor unit and the mechanical force transmitting means, respectively. 14 (A) (B) (C) (D)
(E) is a figure showing the modification which arrange | positions the sensor part of a flow velocity detection device with respect to the flow direction of a fluid.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Suma Matsui Inventor, Suma Matsui, 1-1, Showa-cho, Kariya city, Aichi Prefecture, Nihon Denso Co., Ltd. (56) References -161572 (JP, U) Actually opened Sho 57-122573 (JP, U)

Claims (1)

[Claims] 1. An element which generates strain in response to an applied electric field and generates electric polarization in response to stress, mechanical force transmission means coupled to the element for transmitting fluid pressure to the element, and the element. A drive unit for applying an AC electric field to the device, and a detection unit for detecting the phase difference between the voltage applied to the element and the current flowing through the element, and detecting the flow velocity of the fluid according to the phase difference. Characteristic flow velocity detector.