JPS6312922A - Liquid level detector - Google Patents

Abstract

PURPOSE:To protect lead wires connected to a heat-sensitive element and the heat-sensitive element by forming projection parts on a heat radiation surface which contacts the surface of liquid and a heat conduction plate. CONSTITUTION:A couple of projection streaks 6 which are thicker than a positive temperature characteristic thermistor (PTC) 1 are formed on both sides of the PTC. Further, two couples of coupling ribs 9 are formed in the lengthwise direction of a cylindrical heat radiation case 7 whose internal diameter is equal to the width of the heat conduction plate 2 on the internal wall of the case. Then, both heat radiation surfaces of the conduction plate 9 are fitted to the ribs 9 detachably. The PTC 1 is sandwiched between the projection streaks 6 thicker than the PTC 1 and the lead wires 14 and 15 are provided along the couple of projection streaks 6, so the PTC 1 and lead wires 14 and 15 are protected by the projection streaks 6 and never break, fall, and disconnect by contacting other bodies in assembly, thereby performing the assembly smoothly.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid level detector for detecting the fuel level in the fuel tank of an automobile, the oil level in the engine, and the like.

Positive Temperature Characteristic Thermistor (hereinafter referred to as PTC) is a small and highly reliable liquid level detector with no mechanical moving parts.
A liquid level measuring device using a liquid level measuring device existed as shown in Japanese Patent Publication No. 55-688.

In this liquid level measuring device, a large number of PTCs are arranged upwards 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 was like that.

- is trying to do ([1] The liquid level measuring device shown in the above publication detects a sudden increase in the current value due to the sudden drop in electrical resistance when the PTC comes into contact with the liquid and the temperature drops. Since the detected current value changes in stages, it is necessary to narrow the spacing between PTCs in order to make this gradual change small, which inevitably increases the number of PTCs. In addition, in order to avoid thermal interference between the PTCs, a hole is formed in the heat insulating holder, the PTC is fitted into this hole, and a lead wire fitted into the groove of the holder is separately connected to the PTC. This connection increased the number of parts and required more man-hours, resulting in an unavoidable increase in costs.

Furthermore, in the liquid level measuring device, since the holder is made of insulation, two lead wires are required, or one lead wire fitting groove is provided at the back of the holder to expose the PTC from the holder. As a result of this provision, one lead wire is exposed from the holder, which often causes poor contact or disconnection during assembly or use.

The present invention relates to an improvement of a liquid level detector that overcomes these difficulties. A heat-conducting plate comprising: a heat-sensitive element that generates heat and whose electrical resistance value changes according to temperature changes; and a heat-transfer plate having a heat-radiating surface in direct or indirect contact with the liquid and a heating part in contact with the heat-sensitive element; By forming the protrusion, the lead wire connected to the heat-sensitive element and the heat-sensitive element can be protected.

An embodiment of the present invention illustrated in FIGS. 1 to 5 will be described below.

In the wood example, PTCl is used as a heat-sensitive element that generates heat by itself and has a property that its electrical resistance value changes with temperature changes, but in addition to that, a thermistor (NTC), C
A temperature-sensitive semiconductor such as a TR or a platinum resistance temperature sensor may also be used.

The heat conduction plate 2, which also serves as a holding member for PTCl, is a rectangular plate made of aluminum.PTCl is integrally joined to the center of the side surface of the heat conduction plate 2, and the heat conduction plate 2 is located on both sides of the PTCI. A large number of heat insulating holes 3 are provided in the central part in the longitudinal direction and small in the vicinity of the ends, and the distance between them becomes wider as they approach the ends. A heat conductive plate 2 in which each heat dissipation section divided into equal sections over the direction and PTCl are joined
The thermal resistances between the central heating section 5 and the central heating section 5 are approximately equal to each other.

Further, a pair of protrusions 6 are provided adjacent to both sides of the PTCI and extending upwardly from the PTCI to a height slightly higher than the thickness of the PTCI.

Furthermore, on the inner wall 8 of the cylindrical heat dissipation case 7 made of aluminum and having an inner diameter equal to the width of the heat conduction plate 2, two pairs of engagement ribs 9 are protruded along the longitudinal direction at the diametrical position. The heat dissipating surfaces 4 on both sides of the heat conductive plate 2 can be freely engaged with and detached from the engagement rib 9 with a constant pressure during daytime contact.

In addition, a cap 11 made of an electrically insulating material is removably fitted in the opening 10 of the heat dissipation case 7, and the electrode terminals 12 and 13 provided on the cap 11 are connected to the lead wires 14.
．． It is connected to the PTCl and the heat conductive plate 2 via 15.

In addition, on the outer peripheral surface of the opening 10 of the heat dissipation case 7, there is a threaded portion 1.
6 is formed, and the male threaded part 1 of the heat dissipation case 7 is connected to the ji threaded part 19 provided in the opening 18 of the fuel tank 17.
6 is removably screwed through a gasket 20.

Since the embodiment shown in FIGS. 1 to 5 is constructed as described in 1)4, the heat conduction plate 2 is fitted into the engagement rib 9 of the heat dissipation case 7, and the cap 11 is attached to the heat dissipation case 7. When the male screw part 16 of the heat dissipation case 7 is screwed into the opening 10 of the fuel tank 11 and the electrode terminal 12.13 is connected to a power source via an ammeter (not shown), the PTCl generates heat by itself, and heat is conducted from the heating part 5 of the heat conduction plate 2 toward the heat radiation surface 4, and the inner wall 8 of the heat radiation case 7
The heat flows more toward the surface of the heat dissipation case 7.

When the heat dissipation case 7 is immersed in the fuel in the fuel tank 18 and the liquid level LS is high, the surface area of the heat dissipation case 7 cooled by the fuel FIL is large, and the heat dissipation surface 4 of the heat conduction plate 2 is
Since the area is wide, the heat generated by the PTCI is sufficiently removed, the temperature of the PTCI decreases, and its electrical resistance decreases, causing the pointer of the ammeter to swing significantly.

However, as the fuel is consumed and the liquid level LS decreases, the cooling surface area of the heat dissipation case 7 and the area of the heat dissipation surface 4 of the heat conduction plate 2 decrease, so the temperature of the PTCI increases and its electrical resistance increases. As a result, the deflection of the ammeter pointer gradually decreases.

Furthermore, since the PTCl is sandwiched between the protrusions 6 which are higher than the thickness of the PTCI, and the lead wire 14 is attached to the pair of protrusions 6, the PTCI and the lead wire 14 are protected by the protrusions 6, and the assembly process There is no chance of breakage, falling off, or disconnection due to contact with other objects inside, making assembly work easier and smoother, and productivity improved.

Roughly, the PTCI is tightly packed between the heat dissipation case 7 and the cap 11.
Since it is coated with aluminum, it does not come into contact with moisture, dust, etc., and stable characteristics can be obtained over a long period of time, resulting in good durability.

Furthermore, PTCl is supported only by the heat conduction plate 2, and the air inside the heat dissipation case 7 serves as a heat insulating layer, so the heat insulating effect is high.

Moreover, since resin is not used as a heat insulating material, no mold is required, and time for drying and curing is not required, resulting in high productivity and cost reduction.

In the embodiment described above, PTCl is disposed at only one location in the center of the heat conduction plate 2, but it may be disposed at a plurality of locations at predetermined distances in the vertical direction of the heat conduction plate 2.

Moreover, if the air inside the heat dissipation case 7 is discharged and the case is covered with a low pressure or vacuum state, the heat insulation properties can be further improved.

In the embodiment shown in FIGS. 1 to 5, the heat dissipation surfaces 4 are formed on both sides of the heat conduction plate 2, and the heat conduction plate 2 is fitted into the engagement rib 9 of the heat dissipation case 7. or a heat conductive plate 2 having a heat dissipation surface 22 on only one side as shown in FIG.
1, and a lead wire protection protrusion 23 and a PTC protection protrusion 24 may be provided on the side opposite to the heat dissipation surface 22.

The heat conduction plate 21, which also serves as one electrode plate, is made of copper, and one side end surface of the heat conduction plate 21 is formed into a planar heat radiation surface 22, and the other side end has heating parts at two places, upper and lower. 25 is arranged, and the other side end surface is formed in a tapered shape so as to approach the heat dissipation surface 22 as it goes up and down from this heating part 25, and two leads are formed with a gap along a part of this taper. Wire protection protrusions 23 are protruded parallel to each other, and PTC protection protrusions 24 are protruded on both sides of the heating section 25, and the PTC protection protrusions 24 are sandwiched between the PTC protection protrusions 24 for heating. A vertically elongated P for displaying the liquid level is provided on one side of the section 25.
One side of TC1 is joined together.

Further, in a portion sandwiched between the heat dissipation surface 22 and the heating section 25, a circular heat insulating hole 26 for increasing thermal resistance is provided between the upper and lower portions of the heat dissipation surface 22 and the portion of the heating section 25 that faces the heat dissipation surface 22.
Thermal resistance between each heat dissipation section and the heating section 25, assuming that three sections are provided at each location and divided into n sections in the vertical direction between the minimum width portion 27 of the heat conduction plate 21. are formed so that they are approximately equal.

Furthermore, a lead wire 128 is fitted between the two lead wire protection protrusions 23, and the lead wire 28 is joined to the PTCI by low temperature soldering or other suitable joining means, and the upper end of the lead wire 28 is joined to the other terminal 30,
One terminal 29 formed at the upper end of the heat conduction plate 21 and the other terminal 30 have a fixed positional relationship, and the heat dissipation surface 22 of the heat conduction plate 21 is left in place. The lead wires 28 are joined together with a heat insulating material 31 made of foamed resin without any gaps, thereby forming a liquid level detector.

This terminal 29,30 is connected to the battery via an ammeter, also not shown.

The embodiment shown in FIGS. 6 to 11 is similar to the embodiment shown in FIGS.
8 is a PTC protection protrusion 24 and a lead wire protection protrusion 2
Protected by 3.

As described above, in the present invention, since the heat-sensitive element and the lead wire can be protected by the protrusion, falling off or damage of the heat-sensitive element and breakage of the lead wire can be prevented, and assembly work can be simplified. can be carried out efficiently and reliably.

[Brief explanation of the drawing]

FIG. 1 is a side view of an embodiment of the liquid level detector according to the present invention installed in a fuel tank, and FIG. 2 is an exploded perspective view thereof.
Bacteria Figure 3 is a! along the ■-■ line in Figure 1. 4 is a vertical sectional side view taken along line IV-IV in FIG. 3, FIG. 5 is a front view of the heat conductive plate in the same embodiment, and FIG. 7 is a side view of the embodiment without the heat insulating material, FIG. 8 is a view taken along the ■-■ arrow in FIG. 7, FIG. 9 is a perspective view of FIG. 7, and FIG. 10 is a front view of the embodiment. 11 is a cross-sectional plan view taken along line X-X line a'3 and line A-A in FIG. 7. 1... PTCI, 2... Heat conduction plate 2.3... Heat insulation hole 3.4... Heat radiation surface 4.5... Heating part 5.6...
Projection 6.7... Heat dissipation case 7.8... Inner wall 8.9.
...Engaging rib 9.1°...Opening 10.11...Cap 11.12.13...Electrode terminal 13.14.1
5...Lead wire 15.16...Male thread part 1G, 17
...Fuel tank 17.18...Opening 18.19...
・Female screw part 19.20...Packkin, 21...Heat conduction plate, 22...Radiation surface, 23...Protrusion for lead wire protection, 24...Protrusion for PTC protection, 25 ...heating section,
26... Insulation hole, 27... Minimum width part, 28...
Lead wire, 29.30...terminal, 31...insulation material,
...fuel, LS...liquid level.

Claims (1)

[Claims] A liquid level detector that is immersed in a liquid to detect the height of the liquid includes a heat-sensitive element that generates heat by itself and whose electrical resistance value changes with temperature changes, and a heat-radiating surface that is in direct or indirect contact with the liquid. and a heat-conducting plate having a heating part that comes into contact with the heat-sensitive element, and the heat-conducting plate is provided with a protrusion that protects the heat-sensitive element and a lead wire connected to the heat-sensitive element. Liquid level detector.