JPS62284217A - Liquid level detector - Google Patents

Abstract

PURPOSE:To decrease the number of components by detecting variation in liquid level by one heat sensing element. CONSTITUTION:While the liquid level LS of fuel L is low and below the lowermost part of a heat radiation surface 12, the heat radiation surface 12 is not cooled by the fluid L, so a PTC 10 for liquid level detection is held at high temperature, the electric resistance of the PTC 10 for liquid level detection is large, and the deflection of the pointer of an ammeter is small. Then when the liquid level LS of the fuel L rises, the part cooled by the fluid L becomes larger upwardly from the lowermost part of the heat radiation surface 12 and the PTC 10 for liquid level detection drops in temperature gradually; and the electric resistance of the PTC 10 decreases and the deflection of the pointer of the ammeter increases. The liquid level of the fluid L is detected from the deflection of the ammeter. Consequently, variation in liquid level is detected over a certain range by one heat sensing element.

Description

[Detailed Description of the Invention] Ll! BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detector for detecting the fuel level in an automobile fuel tank, the oil level in an engine, and the like.

[1] A liquid level measuring device using a positive temperature coefficient thermistor (hereinafter referred to as PTC) as a small and highly reliable liquid level detector without any mechanical moving parts was published in Japanese Patent Publication No. 1988-688. It existed as shown.

In this liquid level measuring device, a large number of PTCs are arranged vertically at predetermined intervals, connected in parallel to a power supply, and the liquid level is measured by detecting changes in the current of this power supply circuit. It had become.

In the liquid level measuring device shown in the above publication, a sudden increase in the current value is caused by a sudden drop in electrical resistance when the PTC comes into contact with the liquid and the temperature drops. , the detected current value changes stepwise. To reduce this stepwise change, it is necessary to narrow the spacing between PTCs, which inevitably increases the number of PTCs and increases costs. High was inevitable.

The present invention relates to an improvement of a liquid level detector that overcomes such difficulties, and is a liquid level detector that is immersed in a liquid and detects the height of the liquid level. A heat-sensitive element that generates heat and whose electrical resistance value changes according to temperature changes, and a heat-conducting plate having a heat-radiating surface in contact with the liquid and a heating part in contact with the heat-sensitive element, each having a fixed length extending in the vertical direction of the heat-radiating surface. By forming the heat conductive plate so that the thermal resistance between the heated part and the heating part has a predetermined characteristic, when the height of the liquid level changes,
It is possible to obtain an electrical output that corresponds to changes in the liquid level height, and it is possible to detect changes in the liquid level height with a single heat-sensitive element over a range longer than the length of this heat-sensitive element. can.

The present invention will be explained in detail with reference to FIGS. 1 to 3.

A heat-sensitive element 1, which generates heat by itself and whose electrical resistance value changes with temperature changes, is integrally joined to a heating part 3 in the longitudinal center of one side of a thin plate-shaped gold JIJ heat conduction plate 2, and the other side of the heat conduction plate 2 is One terminal of the heat-sensitive element 1 is connected to the heat-conducting plate 2, one connection terminal 5 is formed on the upper end of the heat-conducting plate 2, and the other terminal of the heat-sensitive element 1 is connected to a lead wire. 6
One of the connecting terminals 5.7 is connected to the positive terminal of battery B through an ammeter 8, and a predetermined voltage from battery B is connected to the connecting terminal 5.7. By applying this voltage, the heat sensitive element 1 self-generates heat.

Furthermore, considering that the heat dissipation surface 4 of the heat conduction plate 2 is divided into n sections in the vertical direction, each heat dissipation section 4s and 4t is divided into n sections.
, 4■, . . . 4n and the heating section 3 have the same thermal resistance R, respectively.

Furthermore, a portion of the heat conductive plate 2 other than the heat dissipating surface 4 of the heat conductive plate 2 and the heat sensitive element 1 are tightly interspaced with a heat insulating material 9.

This liquid level detector is immersed in the fuel FIL, and the liquid level L of the fuel
Consider the case where S is located at the boundary between the m section and the (m+1> section) of the heat dissipation surface 4.

Ak in the air:! There are m sections of the exposed heat radiating surface 4, and there are (n-m) sections of the heat radiating surface 4 exposed in the fuel tank, so the reciprocal of the total thermal resistance to air A on the heat radiating surface 4 is m - The reciprocal of the total thermal resistance to the fuel L on the heat radiation surface 4 is □.

Also, if the thermal resistance of air A and fuel is R^, Rc, then the reciprocal of the total thermal resistance of air A is -m- The reciprocal of the total thermal resistance of R8 fuel is □.

L Roughly speaking, if the temperature difference between air A and fuel and heat-sensitive element 1 is ΔT, the total heat generation of heat-sensitive element 1 is the sum of P j, t P^, Pt, so Since the thermal resistance R^ of is large and the thermal resistance RL of the fuel FIL is small, if R^ is set to ω and RL is set to 0, then the following equation is obtained.

When m is small, that is, when the liquid level Is is high and the heat of the heat-sensitive element 1 is well removed from the heat-radiating surface 4 of the heat-conducting plate 2 by the fuel, the electric power applied to the heat-sensitive element 1, in other words, The current increases, the product becomes larger, and the liquid level L
This shows that as S decreases, the amount of heat removed by the fuel from the heat dissipation surface 4 of the heat conductive plate 2 decreases, and the current flowing through the heat sensitive element 1 becomes smaller. By measuring with an I ammeter, the liquid level in the fuel tank can be detected.

Friend IJ The embodiments shown in FIGS. 4 to 11 will be described below.

The heat-sensitive element 1, which has the characteristic of self-heating and having an electric resistance value that changes with temperature changes, includes a thermistor (NTC),
Temperature-sensitive semiconductors such as PTC and CTR and platinum moisture-sensing resistors exist, but in this embodiment, PTC1G for liquid level detection is used.

Further, the heat conductive plate 11 which also serves as one electrode plate is made of copper (
One side end surface of the heat conductive plate 11 is formed as a planar heat dissipation surface 12, and the other side end is provided with heating parts 13 at upper and lower 2 (1! if) locations. The other side end surface is formed in a tapered shape so as to approach the heat dissipation surface 12 as it moves up and down from this heating section 13, and on one side of this heating section 13, there is a liquid level detection PTC 10 that is elongated in the up and down direction. One side of the is joined together.

Furthermore, the portion sandwiched between the heat radiation surface 12 and the heating section 13 includes a portion of the heating section 13 that faces the heat radiation surface 12 and a portion of the heat radiation surface 12 that is sandwiched between the heat radiation surface 12 and the heating section 13.
Three circular heat insulating holes 14 are provided in each of the upper and lower two locations to increase the thermal resistance between the heat conductive plate 11 and the heat conductive plate 11.
It is formed so that the thermal resistance between each heat dissipation section, which is considered to be divided into n sections in the vertical direction between the minimum width portion 15 of the heating section 13, and the heating section 13 is approximately equal.

Furthermore, a copper correction electrode 17 is disposed at a predetermined interval on the opposite side of the heat dissipation surface 12 at a location above the heat dissipation surface 12 of the heat conduction PR 11, and the side remote from the heat dissipation surface 12 has a tapered area. A narrow heat radiation surface 18 is formed, and one side surface of a vertically elongated temperature correction PTC 21 is integrally joined to one side surface of a heating part 19 located at the base of this correction electrode 17.

Moreover, the electrode plate 22 constituting the other earth plate of the PTC 10 for liquid level detection and the PTC 21 for temperature correction has a small heat capacity, and the PTC 10 for liquid level detection and the PTC 2 for temperature correction
1i1! ] To avoid thermal interference, use PTC for liquid level detection.
10. The joint portion 23, which is formed by press-molding a copper plate that is thinner than the PTC 21 for temperature correction and comes in contact with the PTC 10 for liquid level detection, extends along the longitudinal direction of the electrode plate 22.

The joint portion 24, which is bent into an L-shape and an L-shape, and is in contact with the temperature correction PTC 21, has its negative width side bent at a right angle, and then its end portion is further bent at a right angle in the opposite direction.

PTC 10 for liquid level detection, PTC 21 for temperature correction, and heat conduction plate 11. Correction electrode 17. The electrode plate 22 is bonded to the electrode plate 22 by low-temperature soldering or other suitable bonding means.

In this way, the heat conductive plate 11. P for liquid level detection is provided on the correction electrode 17 and the electrode plate 22.
A liquid level detector is constructed by sealing the assembly in which the TC 10 and the temperature correction PTC 21 are joined with a heat insulating material 26 made of foamed resin without any gaps.

Also, is it corrected with the electrode terminal 16 of the heat conduction plate 11? l! Correction of the pole 17 The FA pole terminal 20 and the electrode terminal 25 of the electrode plate 22 are connected to an ammeter 27 for indicating changes in the liquid level and a battery 28, as shown in FIG.

Since the embodiment shown in FIGS. 4 to 11 is configured as described above, when the liquid level 1j of the fuel tank is low and is located below the lowest part of the heat radiation surface 12, the heat radiation surface 12
is not cooled by fuel, so PTC for liquid level detection
10 is maintained at a high temperature, the electrical resistance of the PTC 10 for liquid level detection is large, and the deflection of the pointer of the ammeter 27 is small.

As the liquid level LS of the fuel tank increases, the cooling portion by the fuel tank increases from the bottom of the heat dissipation surface 12 upwards.
The temperature of PTC10 for liquid level detection gradually decreases, and the temperature of PTC10 for liquid level detection decreases.
The electrical resistance of the rc io becomes smaller, and the deflection of the pointer of the ammeter 27 becomes larger.

In addition, since the change in electrical resistance of the liquid level detection PTC 10 due to the influence of ambient temperature is corrected by the temperature correction PTC 21, the deflection of the pointer of the ammeter 27 is not affected by the ambient temperature, and the liquid level 1j of the fuel [ can accurately indicate the level of

Further, by using only two relatively small PTCs 10 for detecting the liquid level, it is possible to detect level fluctuations in the fuel level L9, which is many times the length of the PTC 10 for detecting the liquid level.

PT for liquid level detection in response to fluctuations in fuel level LS level
In order to change the temperature of C10 approximately proportionally, the heat conduction plate 11
In this method, a heat insulating hole 14 was provided in a part close to the heating part 13 to increase the thermal resistance, but as shown in FIG. Shape insulation hole 31 is provided, and P for liquid level detection is provided.
The heat insulating holes 31 may be formed to become smaller in size as the distance from the TC 10 increases, or the size of the heat insulating holes 31 may be constant and the arrangement pitch may be changed.

Further, as shown in FIG. 13, the part of the facing surface 34 opposite to the heat radiation surface 33 that is close to the liquid level detection PTC 10 is separated from the heat radiation surface 33, and approaches the heat radiation surface 33 as it moves away from the liquid level detection PTC 10. The heat conductive plate 32 may be formed as shown in FIG.

Further, as shown in FIG. 14, the part of the heat conduction plate 35 that is closest to the heat radiation surface 37 on the side 36 or both sides 36 and closest to the PTC 10 for liquid level detection is deep and wide, and the liquid level can be detected. The cutout portion 38 may be formed to become shallower and narrower as the distance from the PTC 10 increases.

Furthermore, as shown in FIG. 15, the heat dissipation surface 40 exposed from the heat insulating material 41 is narrowed at a short distance from the liquid level detection PTC 10, and becomes wider as the distance increases. 39 may be formed.

In addition, as shown in FIG. 16, a heat insulating material 44 is bonded to the heat dissipation surface 43 of the heat conduction plate 42, and the thickness of the heat insulating material 44 is increased in a portion close to the PTC 40 for liquid level detection.
It may be made to become thinner as the distance from C10 increases.

Furthermore, as shown in FIG. 17, a heat insulating material 48 may be interposed at a portion of the heat conduction plate 45 that is in contact with the liquid level detection PTC 1G on the opposing surface 47 of the heat radiation surface 46.

To summarize and explain the matters explained above, in order to equalize the thermal resistance between each heat dissipation section divided into many equal parts in the vertical direction and the heating part, the implementation shown in Figs. 4 to 11 is carried out. In the example, the embodiment shown in FIG. 12, and the embodiment shown in FIG. 13, a method was adopted in which the cross-sectional area of the heat conduction plate was changed. There is a method of changing the thermal conductivity of the heat dissipation surface using a heat insulating material as shown in FIG. 16, a method of changing the thermal conductivity of the heat radiation surface as shown in FIG. A heat insulating material is placed near the liquid level detection plate C10 as shown in FIG.
There is also a method of changing the thermal conductivity from this heat conductive plate, and a method that combines these methods may also be used.

In the above embodiment, the input of the ammeter 27 is determined based on the liquid level Is of the fuel IL.
Although it was configured to change in proportion to the level change of
In motorcycle tanks where the tank for storing liquid is not rectangular parallelepiped, in order to proportionally display the remaining amount of fuel in the tank, the heat dissipation surface of the heat conduction plate and the heating part equipped with PTC are used. Instead of making the thermal resistance constant, it may be configured to provide the desired characteristics. With such a structure, the remaining amount of fuel in the tank can be accurately displayed.

According to the present invention, since it is possible to obtain an electrical output proportional to the change in the liquid level, it is possible to accurately detect the change in the liquid level.

Furthermore, in the present invention, changes in the liquid level can be detected over a wide range with one heat-sensitive element, so the number of heat-sensitive elements required to detect the liquid level over a wide range can be reduced. In addition, the liquid level detector can be configured with the heat conductive plate and the heat sensitive element, and as a result, the number of parts can be reduced, making it possible to downsize and significantly reduce costs.

[Brief explanation of drawings]

Fig. 1 is a side view showing the operating principle of the liquid level detector according to the present invention, Fig. 2 is its side view, Fig. 3 is its electric circuit diagram, and Fig. 4 is the liquid level detector of the present invention. A front view showing one embodiment,
Figure 5 is a side view with main parts removed, and Figure 6 is the Vl-
Vl line arrow view, Figures 7 and 8 are ■-Vf in Figure 5
The cross section cut along the line ■-■, Figure 9 is
10 is a perspective view of FIG. 5, FIG. 11 is an electric circuit of the same embodiment, FIGS. 12 and 13 are side views of another embodiment of the present invention, and FIG. Figure or first
6 is a perspective view of still another embodiment, and FIG. 17 is a side view of still another embodiment. DESCRIPTION OF SYMBOLS 1... Heat sensitive element, 2... Heat conduction plate, 3... Heating part, 4... Heat radiation surface, 5... Connection terminal, 6... Lead wire, 7... Connection terminal, 8... Ammeter, 9... Heat insulating material, 10... PTC for liquid level detection, 11... Heat conduction plate, 12... Heat radiation surface, 13... Heating part, 14... Heat insulation hole, 15...Minimum width part, 1G...Electrode terminal, 1
DESCRIPTION OF SYMBOLS 1... Correction electrode, 18... Heat radiation surface, 19... Heating part, 20... Correction electrode terminal, 21... P for temperature correction
TC, 22... Electrode plate, 23... Connection □0 joint part, 2
4... Joint portion, 25... Electrode terminal, 26... Insulating material, 21... Ammeter, 28... Battery, 30...
... Heat conduction plate, 31 ... Heat insulation hole, 32 ... Heat conduction plate, 33 ... Heat radiation surface, 34 ... Opposite surface, 35 ... Conduction plate, 36 ... Side surface, 37. ...heat dissipation surface, 38...
Missing part, 39... Heat conduction plate, 40... Heat radiation surface, 41
...Insulating material, 42... Heat conduction plate, 43... Heat radiation surface, 44... Heat insulation material, 45... Heat conduction plate, 46...
Heat dissipation surface, 47... Opposing surface, 48... Heat insulating material.

Claims (1)

[Scope of Claims] 1) A liquid level detector that is immersed in a liquid and detects the height of the liquid level, which includes a heat-sensitive element that generates heat by itself and whose electrical resistance value changes with temperature changes; A heat conductive plate having a heat dissipating surface in contact with the heat sensitive element and a heating section in contact with the heat sensitive element, the thermal resistance between each fixed length portion extending in the vertical direction of the heat dissipating surface and the heating section having a predetermined characteristic. The liquid level detector is characterized in that the heat conductive plate is formed as follows. 2) The liquid level detector according to claim 1, wherein the heat-sensitive element is formed to be elongated in the vertical direction.