JP2544617Y2 - Piezoelectric liquid level sensor - 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 liquid level sensor for detecting whether or not liquid levels of various liquids such as oil for an internal combustion engine and a generator are above a predetermined level.

[0002]

2. Description of the Related Art In a piezoelectric liquid level sensor, a diaphragm is disposed in a liquid-tight manner with one surface exposed to the outside at a lower end opening of a metal protection tube, and a piezoelectric element is attached to an inner surface of the diaphragm. Thus, a bimorph-type liquid sensing unit is configured. Such a level sensor is arranged such that the diaphragm has a height corresponding to a predetermined liquid level, and when the liquid is in a container at a predetermined level or more, since the outer surface of the diaphragm is immersed in the liquid, Due to the liquid pressure, even if an alternating voltage is applied to the upper and lower electrodes of the piezoelectric element, the piezoelectric element cannot vibrate. When the liquid level is lower than a predetermined level, the outer surface of the diaphragm is exposed to the air, and the application of the liquid pressure is released to enable vibration.
Therefore, by detecting this vibration, it is detected that the liquid level of the liquid is below a predetermined level, and this is known.

[0003]

By the way, the piezoelectric liquid level sensor is applied to a place where vibration easily occurs, such as an oil tank of an automobile, as described above. For this reason, external vibration propagates to the diaphragm via the metal protection tube, and is extracted as a noise signal, or vibration at the time of oscillation of the diaphragm leaks out, both of which cause erroneous detection. I was In order to correct this problem, a configuration in which a wavy flexible portion is formed in the metal protective tube has been proposed, but in such a configuration, processing becomes troublesome,
Its blocking effect could not be expected much. The purpose of the present invention is to eliminate such conventional disadvantages.

[0004]

According to the piezoelectric liquid level sensor of the present invention, a diaphragm is disposed in a liquid-tight manner with one surface exposed to the outside at the lower end opening side of a metal protection tube. A piezoelectric element is attached to the inner surface to form a bimorph-type liquid sensing unit, and the piezoelectric element vibrates when the exposed outer surface of the diaphragm is not in contact with liquid to detect the presence or absence of liquid. In the sensor, close the bottom opening of the metal protection tube.
Equipped with a peripheral shape that fits in a closed shape, with metal protection at the lower end
A locking flange is provided around the lower end of the pipe, and
A vertical through hole is formed in the center to insert and support the conductive tube.
And a downwardly opening circular pipe groove is formed.
An insertion hole penetrating vertically is formed at the position inside the circular groove
A rubber damper and a cylinder closely fitted to the circular groove of the rubber damper
Part, and the lower end thereof comes into contact with the locking flange from below.
A connecting flange is provided around the inner surface of the cylindrical hole.
The peripheral plate is joined to the diaphragm on which the piezoelectric element is attached,
The inside of the hole is made liquid-tight, and one side electrode of the piezoelectric element is connected to the conductive tube.
Connected, and the other side electrode of the piezoelectric element on the upper end of the cylindrical part
The connection pins that connect to the
Metal cylindrical base lid that can be inserted into the
And a conductive tube which protrudes from an upper surface of the Gomudanpu,
Connect the lead wires that pass through the metal protection tube to the connection pins, respectively.
It is characterized by having been continued .

[0005]

[Function] A rubber damper is fitted in the lower end opening of the metal protection tube,
Further, the cylindrical portion is fitted in the cylindrical groove of the rubber damper, and the metal cylindrical base lid on which the diaphragm having the piezoelectric element is attached on the lower surface is closely fitted. In such a configuration, when an alternating voltage is applied to the front and back electrodes of the piezoelectric element, the cylindrical base lid to which the periphery of the diaphragm is joined is connected via the locking flange of the rubber damper.
It is connected to the protection tube, so that the rubber damper is locked.
A buffer action occurs at the flange, causing vibration to propagate to the diaphragm and
Vibration leakage, and prevent malfunction as much as possible.
Can be. On the other hand, the piezoelectric liquid level sensor is required to have sufficient liquid tightness because it is immersed in the liquid. By the way, in such a configuration, the flow path of the liquid to the piezoelectric element is between the locking flange of the rubber damper and the connecting flange of the cylindrical base lid. However, even if the liquid flows in from the gap, it is necessary to bypass the inner and outer surfaces of the cylindrical groove and travel a long creepage distance in order for the liquid to adhere to the piezoelectric element. Further, the rubber damper is tightly fitted to the cylindrical portion of the cylindrical base lid by the elastic contact action of the rubber damper. For this reason, the piezoelectric element can be held in a liquid-tight state in the protective tube. Furthermore, in such a complicated configuration
Also, insert a conductive tube through the center of the rubber damper to support it
A vertical through hole is formed and opened downward.
A circular groove is formed, and an insertion vertically penetrates at a position in the circular groove.
A rubber damper with a through hole formed and a cylindrical hole in the cylindrical base lid
Vibration plate with the above-mentioned piezoelectric element adhered to the lower edge
Together, the inside of the cylindrical hole is made liquid-tight, and one side electrode of the piezoelectric element is
Connected to the conductive tube, and a piezoelectric element
A connection pin for connecting to the other electrode of the
Insert the rubber damper into the insertion hole of the rubber damper.
The conductive tube protruding from the top of the
Configuration to connect the lead wire that passes through the inside of the protection tube
The electrical connection between the front and back electrodes of the piezoelectric element and the lead wire
Continuation will be secured.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an example of a piezoelectric liquid level sensor S according to the present invention. Reference numeral 1 denotes an elongated protective tube made of a corrosion-resistant metal material such as stainless steel, and a sensor case 2 is fitted over the protective tube 1. The receiving end 3 is externally fitted. The planar shape of the sensor case 2 is elliptical, and a printed circuit board 5 is vertically fitted to the elliptical portion along the long axis, and a protective fitting tube is formed by a circular fitting end 3 coupled to the case 2. 1 can be connected. A male screw is formed on the peripheral surface of the fitting end 3 to facilitate attachment to an oil tank or the like. Various circuit members are mounted on the printed circuit board 5 and are connected to external devices by lead wires 6. Then, lead wires 7a and 7b electrically connected to electrodes of a piezoelectric element 31 described later are inserted through the inside of the protective tube 1 and connected to required conductive paths of the printed circuit board 5.

Next, the main part of the present invention will be described with reference to FIGS. A rubber damper 1 made of a material such as fluororubber or NBR, which is opened downward, is provided at a lower end opening 1a of the protective tube 1.
0 is inserted. The rubber damper 10 has a short cylindrical shape, and has a circular tube groove 11 that opens downward from the lower surface to the inner depth. Annular crimped ridges 12 are formed on the inner peripheral surface of the circular pipe groove 11 at two upper and lower portions. A through hole 13 is formed at the center thereof, and an insertion hole 14 penetrating through the upper surface is connected to a part of the circular tube groove 11. A conductive tube 17 is fitted in the through-hole 13 to secure a conductive path as described later. At the lower end, a locking flange 15 is formed which is in contact with the peripheral end of the lower end opening 1a.

The rubber damper 10 has a metal cylindrical base lid 2.
0 is fitted. The cylindrical base lid 20 is provided with the circular pipe groove 11.
The cylindrical portion 21 is provided at the upper end of the cylindrical portion 21. A press-contact convex ring 22 is formed at the upper end of the cylindrical portion 21. This cylindrical portion 21
Is the same as the depth of the cylindrical groove 11. A connecting flange 23 is formed on the outer periphery of the lower end of the cylindrical base lid 20 so as to vertically contact the locking flange 15.

A diaphragm 30 made of a thin metal plate is provided at the lower end of the cylindrical base lid 20 so as to shield the cylindrical hole 24 from below.
Are arranged with their peripheral edges joined. This diaphragm 3
At the center of the inner surface of the piezoelectric element 0, a piezoelectric element 31 constituting a liquid sensing part together with the diaphragm 30 is fixed. The piezoelectric element 31
Are made by arranging electrodes on the front and back surfaces of a piezoelectric ceramic disc made of lead zirconate titanate or the like. The piezoelectric element 31 is disposed so as to face the inside of the cylindrical hole 24. Although the piezoelectric element 31 having such a configuration has a two-terminal structure, a three-terminal structure having a large-area excitation electrode and a small-area feedback electrode on the surface side may be used.

A connecting pin 25 projects from the upper end of the cylindrical portion 21 of the cylindrical base cover 20, and is electrically connected to the back electrode of the piezoelectric element 31 via the diaphragm 30 and the metal cylindrical base cover 20. Connected.

The procedure for assembling the components will be described. The cylindrical base lid 20 to which the diaphragm 30 is fixed is a rubber damper 10
The cylindrical portion 21 is fitted in the circular pipe groove 11. At this time, the connection pins 25 are inserted into the insertion holes 14 of the rubber damper 10 from below. As a result, the press contact convex ring 22 is
Inside, it is in close contact with the inner and outer surfaces of the circular tube groove 11, and
2 is pressed against the inner surface of the cylindrical portion 21, so that the cylindrical portion 21 is closely fitted in the cylindrical groove 11, and the connecting flange 23 is pressed against the lower surface of the locking flange 15 of the rubber damper 10. .

The surface electrode of the vibrating plate 30 has a conductor 3
3 are connected in advance, and at the time of the above-described fitting, the conductive tube 17 is inserted from the other end into the conductive tube 17 at the upper end position.
Is electrically connected by soldering to the tip of the lead, and the remaining lead end is cut.

After the rubber damper 10 and the cylindrical base cover 20 are integrated as described above, the protective tubes 1 are inserted through the printed circuit board 5 to draw out the leads 7a, 7b. The lead wire 7 b is connected to the peripheral surface by soldering, and the lead wire 7 b is connected to the protruding end of the connection pin 25 from the insertion hole 14. The front surface electrode of the piezoelectric element 31 is connected to a required conductive path of the printed circuit board 5 via the conductive wire 33, the conductive tube 17, and the lead wire 7a.
0, the cylindrical base lid 20, the connection pins 25, and the lead wires 7b are connected to required conductive paths of the printed circuit board 5, respectively. After the electrical connection is made in this manner, the rubber damper 10 to which the tubular base lid 20 is fitted is fitted inside the lower end opening 1a of the protective tube 1. At this time, each member is held tightly in the protective tube 1 by the elastic contact of the rubber damper 10.

In such a configuration, the lead wires 7a, 7
Since b is not directly connected to the piezoelectric element 31, vibration is not transmitted to the piezoelectric element 31 by propagating through the lead wires 7a and 7b, and the load of the lead wires 7a and 7b is directly applied to the piezoelectric element 31. Never even.

The above-structured piezoelectric liquid level sensor S
In this case, the fitting end 3 is fixed by means such as screwing into a screw of an oil injection port provided on the outside of the oil tank. At this time, the lower end is set to the position of the reference level of the oil.

In this piezoelectric liquid level sensor S, an alternating voltage is applied to the front and back electrodes of the piezoelectric element 31 from the lead wires 7a and 7b. When the liquid in the oil tank is at or above the reference level, the lower end of the protective tube 1 is immersed in the oil. For this reason, the diaphragm 30
Because of the hydraulic pressure of the oil, even when an alternating voltage is applied to the piezoelectric element 31, its vibration is suppressed, and the sharpness of the resonance impedance characteristic is reduced. Further, when the oil level is lower than the reference level, the diaphragm 30 is exposed to the air, and vibrates greatly with the application of the alternating voltage to the piezoelectric element 31. For this reason, the sharpness of the resonance impedance characteristic becomes high, and a change in the resonance sharpness can be detected to reduce the level, and a warning display on an external display such as a warning lamp becomes possible.

Since the piezoelectric liquid level sensor S is applied to a place where vibration is likely to occur, such as an oil tank of an automobile, as described above, external vibration propagates through the metal protection tube 1. And a part of the vibration generated by the oscillation of the diaphragm 30 leaks to the tank side through the protective tube 1. However, the cylindrical base lid 20 to which the vibration plate 30 is fixed is connected to the protective tube 1 via the locking flange 15 of the rubber damper 10, and thus the locking flange 15 of the rubber damper 10 is connected. As a result, a shock-absorbing action is generated, vibration propagation to the vibration plate 30 and vibration leakage from the vibration plate are suppressed, and malfunction can be prevented as much as possible.

The present embodiment has the following sealing effect. That is, the flow path of the liquid to the piezoelectric element 31 side is between the locking flange 15 of the rubber damper 10 and the connecting flange 23 of the cylindrical base cover 20, as shown by the arrow in FIG. However, even if the liquid flows from such a gap, in order for the liquid to adhere onto the piezoelectric element 31, the liquid is detoured around the inner and outer surfaces of the cylindrical groove 11 as indicated by arrows, and is increased by the crimping ridges 12, 12. The liquid that has to travel along a long creepage distance must be passed along the surface of the circular pipe groove 11 and is squeezed out by the convex ring 22 and the pressure ridges 12, 12. Further, the rubber damper 10 is tightly fitted to the cylindrical portion 21 of the cylindrical base lid 20 by the elastic contact of the rubber damper 10. For this reason, the piezoelectric element 31 can be held in the protective tube 1 in a liquid-tight manner.

[0019]

[Effects of the Invention] As described above, the present invention provides a metal protection tube 1
A rubber damper 10 having a circular pipe groove 11 opening downward is fitted in the lower end opening 1a of the piezoelectric element 31.
Since the metal cylindrical base lid 20 having the vibration plate 20 provided with a liquid-tight shape is fitted to the rubber tamper 10 by tightly fitting the cylindrical portion 21 in the circular pipe groove 11. Due to the shock-absorbing action of the rubber tamper 10, the metal protection tube 1 does not require any metal processing, and the vibration propagation from the outside and the vibration leakage from the diaphragm are cut off, and the malfunction can be eliminated as much as possible. Further , the creepage distance along which the liquid travels along the surface is increased by the circular pipe groove 11, and the cylindrical base lid 20 is tightly fitted with the elastic contact of the rubber damper 10, so that the rubber damper 10
Even if the liquid flows from between the cylindrical base lid 20 and the liquid, the flow of the liquid is sufficiently shut off, the liquid tightness of the piezoelectric element 31 is improved, and the rubber damper 10 is tightly fitted to the lower surface of the protective tube 1.
There are excellent effects such as stable holding.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional side view of a piezoelectric liquid level sensor S of the present invention.

FIG. 2 is a perspective view showing a rubber damper 10 and a cylindrical base lid 20 separately.

FIG. 3 is an enlarged vertical sectional side view of a main part.

[Explanation of symbols]

 S Piezoelectric liquid level sensor 1 Protective tube 10 Rubber damper 11 Circular groove 15 Locking flange portion 20 Cylindrical base lid 21 Cylindrical portion 23 Connecting flange portion 24 Cylindrical hole 25 Connection pin 30 Vibration plate 31 Piezoelectric element

Claims (1)

(57) [Scope of request for utility model registration] 1. A bimorph type liquid sensing device in which a diaphragm is disposed in a liquid-tight manner with one surface exposed to the outside at a lower end opening side of a metal protection tube, and a piezoelectric element is attached to an inner surface of the diaphragm. A piezoelectric liquid level sensor configured to vibrate the piezoelectric element when the exposed outer surface of the vibration plate is not in contact with a liquid to detect the presence or absence of a liquid . The peripheral shape to be fitted
A locking flange which abuts the lower edge of the metal protection tube at the lower end thereof
Section is provided around the center, and a conductive tube is inserted and supported in the center.
Vertical through holes are formed and open downward
Is formed, and penetrates up and down at a position inside the circular tube groove.
A rubber damper having an insertion hole formed therein, and a cylindrical portion closely fitted to a circular groove of the rubber damper.
A connecting flange is provided at the lower end to be in contact with the locking flange from below.
And the piezoelectric element on the inner surface at the edge of the cylindrical hole.
The peripheral edge of the diaphragm to which the is attached is joined to make the inside of the cylindrical hole liquid-tight.
Connecting one side electrode of the piezoelectric element to the conductive tube,
Is connected to the other end of the piezoelectric element at the upper end of the cylindrical part.
Pins, and insert the connection pins into the insertion holes of the rubber damper.
And a metal tubular base cover made so as to enter a conductive tube that protrudes from the upper surface of the Gomudanpu, connecting pins
Connect the lead wires that pass through the metal protection tube to
Piezoelectric liquid level sensor, characterized in that there was Unishi.