Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2002-03-27
2004-04-20
Decady, Albert (Department: 2858)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C324S699000, C324S713000, C324S723000, C324S716000
Reexamination Certificate
active
06724201
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a resistance-type liquid level measuring apparatus installed in a fuel tank, for detecting a liquid level by a resistance value of a resistor corresponding to a contact position of a movable contact interlocked with a float floating on the surface of a liquid.
BACKGROUND ART
In a vehicle traveling by a fuel such as gasoline or methanol, a fuel tank for containing the fuel is mounted, and an engine is driven by fuel supply from this. A fuel gauge indicating the residual quantity of such fuel is installed in a dashboard in front of a driving seat, and a driver confirms this to judge lack of fuel and carries out refueling.
As a fuel gauge for indicating the residual quantity of fuel in a fuel tank as stated above, a cross coil-type instrument using a pointer for indication, a stepping motor-type instrument, a liquid crystal indicator using a bar graph or a digital numerical value for indication, a fluorescent display tube, or the like is used. As a detector for detecting the residual quantity of fuel in a tank, a liquid level sensor is generally known in which a resistance-type sensor, which has a simple structure and is inexpensively constructed, is installed in a fuel tank, and a driver in a driving seat can always confirm the fuel residual quantity indicated by this fuel gauge during the driving, and can judge the necessity of refueling according to a distance to a destination.
In the detection of a fuel residual quantity by a fuel gauge made of such a resistance-type sensor, a movable contact is angularly rotated by an arm coupled with a float floating according to a liquid level, or a contact position is vertically moved by a contact fixed to a ring float, and a resistance value corresponding to the liquid level is obtained through a voltage at a connection position to many conductor electrodes connected with a resistor on an insulating substrate. However, since the position of the contact is changed in a state where it is immersed in the fuel such as gasoline or methanol, and since an electric current is applied to the contact portion, there is a possibility that a problem of contact abrasion or contact fault arises at the contact portion, and it has been improved by the improvement of a contact material. As disclosed in, for example, Japanese Utility Model Publication No. Hei. 4-1682, it is known that such a conductor electrode is made of a mixture of AgPd (silver palladium) powder and glass, and is obtained by mixing Ag (silver) powder, palladium (Pd) powder, and glass powder to form a paste, printing it on an insulating substrate, drying this, and then, firing. Ag (silver) has a low electric resistance and is excellent in conductivity, however, when used in a fuel, it is degraded or corroded by, for example, sulfur, moisture, alcohol, or the like in the fuel, and causes defective continuity.
Especially in a fuel such as bad gasoline, an Ag (silver) component of an electrode or a contact is sulfurized by sulfur in the fuel, and silver sulfide is deposited on the electrode or the contact surface, so that electric resistance between contacts is increased to influence an electric current flowing between the contacts. In a detection system of voltage dividing specification as disclosed in, for example, Japanese Utility Model Publication No. Sho. 60-23709, in which a movable contact is grounded or this movable contact is used as an output terminal, an actual divided voltage by a movable contact of a variable resistor can not be obtained by the influence of the resistance between contacts due to such sulfide, and there is such a problem that an error is produced in the indication of a fuel quantity as a fuel gauge. That is, from an E point (low region: empty side) at which a resistance value is at a maximum position to an F point (full tank: full side) corresponding to a minimum position, especially at the F point, electric resistance between contacts is influenced by silver sulfide, and there occurs such a phenomenon that the indication of the fuel gauge does not accurately indicate the F point though full tank refueling is carried out.
By such phenomenon, in a pointer-type instrument, a rather lower side from the F point scale position of a dial is indicated, and in a bar display by a plurality of segments in an electronic indicator such as a liquid crystal indicator, a segment corresponding to the F point does not operate, and segments at the lower side are displayed, so that the indication lacking reliability is produced such that in spite of a full tank, the F point is not indicated. A similar minus indication phenomenon occurs also at the E point side of the low region, however, in this case, the E point is indicated even if some fuel remains, and accordingly, such a situation as running out of gas does not occur and there is no problem in practical use. However, there arise a problem that a distrust is produced at refueling if the indication remains minus at the F point.
Further, such a phenomenon also occurs in a structure used for, for example, a fuel tank of a motorcycle, in which a main tank and a sub-tank are provided, resistance-type sensors are respectively installed in the tanks, and these resistance-type sensors are connected in series with each other to obtain the sum of residual quantities of fuel in both the tanks, and an indication error by the increase of contact resistance due to silver sulfide has a greater influence as the sum of the two resistance-type sensors.
In order to elucidate the mechanism of silver sulfide generation as stated above, the present inventor prepared many resistance-type sensors, immersed them in a liquid containing sulfur, measured a voltage between contacts due to generation of silver sulfide, that is, a voltage drop generated by deposited silver sulfide, and investigated and studied the influence exerted on the indication of a fuel gauge. In the resistance-type sensors of experimental objects, a conductor electrode material contained AgPd and a contact material was an alloy containing CuNi (copper nickel) as its main ingredient, or an alloy containing CuNiZn (copper nickel zinc) as its main ingredient or an alloy containing it. A change of a voltage drop VS between contact points due to the deposition of silver sulfide was measured under the conditions of a power supply voltage V=5 v, a resistance value of a voltage dividing resistance RO=120 &OHgr;, and as a resistance value of a resistor R
1
, 130 &OHgr; at the E point position to 13 &OHgr; at the F point position. As a result, a phenomenon with saturated voltage occurred in which although the voltage drop VS was gradually increased with the degree of deposition of silver sulfide, a further increase was not seen at approximately 0.4 v to 0.6 v. Further, in order to confirm such phenomenon, experiments were repeated in which the deposition of silver sulfide was advanced and the power supply voltage V was changed. As a result, it was found that the voltage became constant at approximately 0.4 v to 0.6 v, and a further increase did not occur. This is because a current application mechanism through silver sulfide deposited on the electrode surface operates as a semiconductor to cause a function just like a diode, and it appears that a constant voltage drop phenomenon of 0.4 v occurs irrespective of the quantity of the deposition and irrespective of the magnitude of the power supply voltage. Incidentally, even if AgPd (silver palladium) alloy, AgCu (silver copper) alloy, AgNi (silver nickel) alloy or the like is used as the contact material, the voltage drop VS to the deposition of silver sulfide becomes also about 0.4 v by the same function.
With respect to such voltage drop VS=0.4 v, in the case where a detection voltage VO is obtained at a connection point between a voltage dividing resistance RO and a resistor R
1
under a power supply voltage V=5 v, the detection voltage is VO=(5−0.4)×R
1
/(RO+R
1
)+0.4, and when a voltage equivalent to a full tank of a liquid level is VF,
Enomoto Kiyoshi
Sato Koichi
De'cady Albert
Kerveros James
McDermott & Will & Emery
Nippon Seiki Co. Ltd.
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