JPH04208817A - Residual fuel amount detector for vehicle - Google Patents

Abstract

PURPOSE:To enhance reliability in the detection of the residual amount of fuel by a method wherein a large number of resistors each having a high temp. coefficient connected in series/parallel are received in a fuel tank to be subjected to self-heating and the change of resistance values due to the temp. difference generated by the up and down movement of a liquid level is detected. CONSTITUTION:A liquid level detector 8 is constituted by parallelly connecting resistor groups 3 each formed by connecting a plurality of resistance temp. sensors 1, 2 having high and low resistance temp. coefficients in series and received in a fuel tank. The reference potential generated by a reference potential generating part 6 is set so as to be higher than the potential of the resistors in a liquid but lower than that of the exposed resistors and compared with each of the potentials of the resistor groups by a comparator 7. The value of the current flowing to a signal wire 9 corresponding to the output signal of the comparator is detected by a current detection part 12 and the number of the resistors in the liquid is confirmed on the basis of the current value to detect a liquid level. By this constitution, a simple and highly reliable detector can be obtained.

Description

[Detailed description of the invention]

[00011

[Field of Industrial Application] The present invention relates to a fuel remaining amount detector for an automobile, which detects the remaining amount of fuel in a fuel tank of an automobile or the like. [0002] Conventionally, this type of fuel remaining amount measuring method has generally used a sliding contact potentiometer attached to the end of a liquid level float. [0003]

[Problems to be Solved by the Invention] In the conventional configuration using such a potentiometer, the contact point is in the fuel liquid,
Otherwise, due to exposure to steam, sulfides and other additives contained in the fuel may cause contact failure, making it difficult to maintain a correct sliding resistance value over a long period of time. [0004] In order to solve the above-mentioned problem, as shown in FIG. 4, a plurality of self-heating temperature-sensitive resistors 15 having a large resistance temperature coefficient are separated in multiple stages on a support substrate 14 to generate heat by energization. Resistor 1 with a small resistance temperature coefficient
6 is connected in series to each temperature-sensitive resistor 15, and a group of resistors connected in series are connected in parallel to form a thermal fuel remaining amount detector. [0005] In terms of the circuit, as shown in FIG. 5, a temperature-sensitive resistor 15 that generates heat when energized and a resistor with a small temperature coefficient of resistance are mounted on a support substrate 14 parallel to the fuel liquid level or at a certain level with the liquid level. It consists of a liquid level detecting section having temperature sensitive elements arranged in multiple stages separated by an angle, and a liquid level detecting circuit that circuit-processes and outputs the signal detected by this liquid level detecting section. When the fuel liquid level reaches the relevant temperature-sensitive resistor 15, the temperature-sensitive resistor 15, which has been energized and generates heat, is immediately cooled down, and a resistance value change occurs at that liquid level, resulting in a change in the differential output voltage. Fluctuations are detected by the comparator 17 of the liquid level detection circuit, and the output of this comparator is processed as a signal by the Nijicorder ICl3, thereby instantaneously detecting the fuel level. [0006] However, the liquid level detection circuit using the encoder ICl3 is not very preferable in practice. This is because the liquid level detection unit 19 must be placed in the fuel, and the liquid level detection circuit 20 must be placed at the top of the fuel tank so as not to come into direct contact with the fuel. In this case, 13 connection lead wires are required. This type of wiring is difficult to implement due to cost considerations, and the longer the lead wires, the more susceptible to the effects of noise. Therefore, the liquid level detection circuit must be installed inside the fuel tank or installed on the same board as the liquid level detection circuit. It has no choice but to be placed on top. [0007] Therefore, when considering a configuration in which the encoder ICl3 is immersed in fuel, the configuration is such that multiple (12 in this example) comparator outputs are signal-processed by one (1 in this example) encoder ICl3. Therefore, if this encoder ICl3 were to fail, it would become impossible to simultaneously process signals from a plurality of comparator outputs, and there is a risk that the fuel level would not be detected at all. When used to detect the remaining amount of fuel in an automobile, failure to detect it is particularly unacceptable. [0008] Also, since the signal output from the encoder ICl3 is a binary code (hereinafter referred to as BCD output), the output signal line of the thermal fuel level detector is normally 4.
However, it is difficult in terms of cost to draw out 4 to 6 signal lines from the fuel tank to the remaining fuel level indicator (residual level gauge) inside the vehicle cabin. Therefore, in order to reduce the number of output signal lines to one (excluding the GND line), the BC
The signal converted to D output is sent to D/A converter 2.
1, it is necessary to reconvert it into an analog signal again. However, installation of this D/A converter 17 is also difficult to realize due to cost considerations. [0009] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a thermal fuel remaining amount detector that ensures reliability of remaining fuel amount detection and is inexpensive in terms of cost. [00101

[Means for Solving the Problem] In order to achieve the above object, the present invention separates a plurality of self-heating temperature-sensitive resistors having a large resistance temperature coefficient on a support substrate in multiple stages. The liquid level detection section is constructed by connecting a resistor with a small resistance temperature coefficient in series to each temperature-sensitive resistor to form a resistor group, and connecting these resistor groups in parallel. and a first reference potential generation section that is connected in parallel with the detection section and generates a temperature-compensated first reference potential;
The voltage comparator is comprised of a plurality of voltage comparators corresponding to each temperature-sensitive resistor group and outputs an on/off output signal by comparing the potential of each temperature-sensitive resistor group with the first reference potential. The output side of the voltage comparator includes a comparator connected to one signal line, a second reference potential generator that applies a constant second reference potential to the signal line, and The present invention is characterized by comprising a current detection section that detects a current value flowing from the signal line to the comparison section, and a display section that displays the remaining amount of fuel by displaying the output from the current detection section. . [00111] [Operation] According to the present invention, since each voltage comparator is independent of each other, even if one voltage comparator fails due to being immersed in fuel, only a slight error will occur. in,
Unlike the conventional case where the encoder IC malfunctions, detection will not be significantly distorted or detection will not be possible. Further, the output signal from the comparison section is also an analog signal, and there is one signal line, and the number of signal lines between this signal line and the current detection section, and between the current detection section and the display section is also one, The number of signal lines can be significantly reduced. Therefore, the influence of noise can be drastically reduced. Therefore, the remaining amount of fuel in an automobile, etc. can be detected with high reliability and accuracy without contact. [0012] [0012] Hereinafter, one embodiment of the present invention will be described with reference to the drawings. [0013] FIG. 1 is a circuit diagram of a remaining fuel amount detector according to an embodiment of the present invention. The liquid level detection part is a temperature-sensitive resistance element 1 (resistance value 100Ω) that generates heat when energized and has a large resistance temperature coefficient.
) with a small resistance temperature coefficient chip resistor 2 (resistance value 60
Ω) are connected in series, and 16 resistor groups 3 are connected in parallel. [0014] Furthermore, the first reference potential generating section 6 is located at the lowest part of the resistor group 3, and is normally immersed in the fuel liquid. The resistor group 3 is composed of a temperature compensating element 4 and a chip resistor 5 having a small temperature coefficient connected in series with the temperature compensating element 4.
are connected in parallel. Note that the temperature compensation element 4 has almost the same resistance temperature coefficient as the temperature sensitive resistance element 1. Further, since the resistance value is 2Ω, which is 20 times that of the temperature-sensitive resistance element 1, self-heating can be ignored, and a reference potential Vo is generated according to the atmospheric temperature inside the fuel tank. [0015] Sixteen voltage comparators 17 are provided corresponding to each resistor group 3, each with a positive (non-inverting input)
The potential of each temperature-sensitive resistance element 1 is input to the side, and the reference potential Vo (first reference potential) of the temperature compensator is input to the negative (inverted input) side, and the liquid level is detected by comparing these voltages. . The liquid level detection section and the comparison section (
The portion indicated by 8 in the figure) is immersed in the fuel liquid. (0016) The output characteristics of the temperature-sensitive resistor group with respect to the liquid level are shown in Figure 2.
As shown in (a) and (b). Among the 16 resistor groups 3, the portion completely immersed in the fuel liquid loses the self-generated heat to the liquid, so the potential is equal to the reference potential Vo.
(See FIG. 2(a)). Therefore, the output of voltage comparator 7 becomes low (ON). On the other hand, resistor group 3, which is completely exposed from the liquid surface, generates heat due to self-heating due to energization.
The potential rises and becomes larger than the reference potential Vo, and the output of the voltage comparator 7 becomes high (OFF) (see FIG. 2(b)).
. [0017] Based on this principle, each voltage comparator 7
A limiting resistor 7a (resistance value is R1) is connected to the output side of each voltage comparator 7, and the other end of this limiting resistor 7a is connected to one signal line 9. This is a connected configuration. The signal line 9 is applied with the same potential V as the second reference potential generating section 11 (potential V,) via the operational amplifier 10. Here, when the output of the voltage comparator 6 is high, the current flowing from the signal line 9 to the limiting resistor 7 becomes 0, and when it is low, (V, -V,) /
A current corresponding to R+ flows. However, this o is a dropout voltage due to the ON resistance of the voltage comparator 6, and normally varies as vo = 0.2 ± 041V, but by increasing the second reference potential V, the error can be reduced and it is suitable for practical use. Can be ignored. In this way, the current IOU flowing from the signal line 9 to the comparison section changes depending on the number of voltage comparators 6 whose output is low (ON) (the number of temperature-sensitive resistance elements 1 immersed in the fuel liquid). It is something. Then, in conjunction with this, the current value flowing through the resistor provided between the collector of the transistor connected to the output side of the operational amplifier 10 and the signal line 9 is detected by the current detection section 12. Then, the output from the current detection section 12 is guided to the display section 13 and displayed. [0018] In this embodiment, the values of R1 of the limiting resistor 7 are all the same resistance value, so unless the fuel tank is a rectangular parallelepiped, the output data will be a linear output as shown in FIG. 3(b). However, weighting is performed by changing the value of R1 and the value of the suction current flowing to the voltage comparator 6, and the output characteristics (relationship between liquid level and remaining amount) can be linearized even for irregularly shaped fuel tanks. It is possible (Figure 3 (
a)). [001,9] By the way, in this embodiment, the resistance values of the temperature sensitive resistance elements 1 for level detection are all 100Ω, but it is not necessary that they all have the same resistance value. Further, the number of temperature-sensitive resistance elements 1 in the resistor group 3 is not particularly limited to 16, and the circuit may be configured by combining any number of resistance elements as necessary. [00201Also, although the entire remaining fuel amount detector is immersed in fuel, the main component is ruthenium oxide, which has been used in conventional float-type remaining fuel amount detectors by being immersed in the fuel tank. A fixed resistor with a dense glass overcoat is used for the resistor, which protects the resistor from sulfides in the fuel, so there is no problem with reliability. Reliability can be significantly improved compared to IC. Furthermore, even if one of the voltage comparators 6 were to fail, it would only cause a small error, but the detection would not be significantly erroneous or become undetectable, as would be the case if the encoder ICl3 were to fail. . Furthermore, since the output signal of the detection circuit according to the present invention is an analog current output, only one output signal line is required. Therefore, the remaining amount of fuel in an automobile, etc. can be detected with high reliability and accuracy without contact. [00211] [Effects of the Invention] As described above, according to the present invention, the output signal is an economical analog current output, so only one signal line is required, it is resistant to noise, and the output signal is extremely simple. At the same time, it also has the effect of being able to be linearized. Therefore, the remaining amount of fuel in an automobile or the like can be detected with high reliability and accuracy without contact.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a fuel level detector for an automobile according to an embodiment of the present invention.

[Figure 21 (a) is an output characteristic diagram of the liquid level detection section that is completely immersed in fuel in the same embodiment. (b) is an output characteristic diagram of the liquid level detection section that is not completely immersed in fuel in the same embodiment [
FIG. 31 (a) is an output characteristic diagram showing the linearized remaining amount of fuel in the same example. (b) is an output characteristic diagram showing the remaining fuel amount that is not linearized in the same example.
Figure 4: A plan view showing the liquid level detection part of a conventional fuel level detector

[Figure 5] Circuit diagram of the detector

[Explanation of symbols]

1 Temperature-sensitive resistance element 2 Chip resistor 3 Resistor group 4 Temperature compensation element 5 Chip resistor 6 First reference potential generation section 7 Voltage comparator 7a Limiting resistor 8 Liquid level detection part and comparison part 9 Signal line 10 Operational amplifier 11 Second reference potential generation section 12 Current detection section 13 Display section

[Figure 4]

Claims (1)

[Claims] 1. A plurality of self-heating temperature-sensitive resistors with large resistance temperature coefficients that generate heat when energized are arranged separately in multiple stages on a support substrate, and each temperature-sensitive resistor has a small resistance temperature coefficient. A liquid level detecting section is connected in series to the body to form a resistor group, and a liquid level detecting section is constructed by connecting these resistor groups in parallel. A first reference potential generating section that generates a reference potential, and a corresponding to each temperature-sensitive resistor that compares the potential of each temperature-sensitive resistor group with the first reference potential and outputs an on/off output signal. The output side of the voltage comparators is composed of a plurality of voltage comparators connected together to one signal line, and a second reference potential generator that applies a constant second reference potential to the signal line. a current detection unit that detects a current value flowing from the signal line to the comparison unit according to the number of on/off states of the voltage comparator; and a current detection unit that displays the output from the current detection unit to display the remaining amount of fuel. 1. A fuel remaining amount detector for an automobile, comprising a display section that performs the following actions.