JPH0434428Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a detection circuit for an oil level sensor that detects the level of lubricating oil or hydraulic oil in an engine and its auxiliary equipment.

Conventional technology A conventional liquid level detector is, for example,
As shown in the publication, one end of the cylinder is attached to the liquid port plug, a detection tube is fixed to the other end of the cylinder, and a lead plug is inserted into the inside of the cylinder and connected to the end of the lead wire. It has a structure in which a detection electrode is attached to a cylindrical body.

Furthermore, the liquid level detection device disclosed in Japanese Patent Publication No. 58-28530 generates oscillations from an oscillator for reference oscillation and an oscillator for measuring the liquid level that includes the interelectrode capacitance detected by the liquid level sensor. It has a configuration that allows accurate measurement of the liquid level by detecting the difference in oscillation frequency between the two. A liquid level sensor forms an inter-electrode capacitance between an outer cylinder and an inner cylinder made of a conductive material such as aluminum or copper, and when the liquid level sensor is immersed in the liquid to be measured, The difference in capacitance between the outer cylinder and the inner cylinder can be detected as the liquid level based on the difference between the dielectric constant of the liquid and the dielectric constant of the part other than the liquid to be measured. However, this liquid level detection device requires high precision and a complicated circuit.

Further, Japanese Patent Publication No. 60-35613 discloses a liquid level gauge in which an electrode is fitted into a hole formed in a sleeve, and the insulating sleeve is further inserted into a hole in a conductive protective tube. When this liquid level gauge is immersed in liquid, a current flows between the electrode and the conductive protection tube, and when the liquid level drops, the amount of current decreases and the liquid level can be detected.

Liquid level detection is commonly performed by sensing the capacitance of the liquid and the sensing electrode tube and by directly sensing the conductivity of the liquid. For level sensors that detect capacitance, the detection level depends on the dielectric constant of the liquid, and for level sensors that detect conductivity, the detection level depends on the conductivity of the liquid. Furthermore, in the case of detecting capacitance, the detection circuit configuration is complicated, and the entire device becomes expensive. In addition, it is difficult to detect liquids with extremely high insulation resistance, such as oil, based on conductivity. In particular, some lubricating oils or hydraulic oils for engines and their auxiliary equipment have extremely high insulation resistance, and
Because of the temperature dependence shown in the figure, it has been difficult to detect the oil level by direct detection of electrical conductivity. In addition, in the figure, the horizontal axis shows oil temperature, the vertical axis shows insulation resistance, a shows the characteristics of high insulation oil, and b shows the characteristics of low insulation oil.

Problems to be Solved by the Invention A circuit for detecting minute currents is required to detect the level of a liquid with extremely low conductivity. Conventionally, a circuit for detecting minute currents uses an operational amplifier 16 connected to a feedback resistor 11, as shown in FIG. 6, for example. A voltage divided by resistors 12 and 13 is supplied to the non-inverting input terminal of the operational amplifier 16, and a variable resistance element 14 such as a high impedance optical sensor is connected to the inverting input terminal. Here, if the current flowing into the operational amplifier 16 is Iin, the input voltage of the operational amplifier 16 is Va, and the resistance values of the feedback resistor 11 and element 14 are Rf and Rx, respectively, the output voltage of the operational amplifier 16 is
The relationship between Vo and these is Vo＝Va＋RfIin＋Rf／Rx・Va.
Therefore, as the resistance value of the variable resistance element 14 changes,
The output voltage Vo of the operational amplifier 16 changes. This circuit is suitable for detecting changes in the resistance value of the variable resistance element 14 of about several MΩ (megaohms).
It is not suitable for detecting the level of various oils used in vehicles operated in extremely cold regions.
In extremely cold areas with temperatures as low as -50°C, the insulation resistance of the oil
Since the resistance reaches 500 GΩ (gigaohms) or more, the presence or absence of oil cannot be detected with conventional circuits. Furthermore, conventionally, most methods of detecting the level of liquids with extremely high resistance such as oil have utilized electrostatic capacitance, and there have been no simple circuits that utilize conductivity for detection.

The object of the present invention is to provide a detection circuit for an oil level sensor that has a simple circuit configuration and can be used even in extremely cold regions.

Means for Solving the Problem First and second resistors connected in series to a DC power supply and dividing the DC power supply voltage, and a second resistor connected to the DC power supply and having a resistance value of 1 GΩ (giga ohm) or more. 3, one electrode connected in series to the third resistor, the other electrode arranged to be energized via oil, and the third resistor. and one input terminal connected to the connection point of the one electrode and the other input terminal connected to the connection point of the first and second resistors, and the first and second resistors A DC power supply voltage divided by is input as a reference voltage to the other input terminal, and a fluctuating voltage based on a change in insulation resistance between the other electrode and the one electrode is input to the one input terminal. , and an operational amplifier that generates an output voltage that changes depending on a change in potential difference between the other input terminal and the one input terminal.

Function: DC power supply voltage +Vcc is divided by resistors 2 and 3 to form a reference voltage. A resistor 4 of 1 GΩ or more is connected between one electrode 5 and a DC power supply,
An insulation resistance is formed between one electrode 5 and the other electrode 8 which is arranged to be electrically conductive with respect to one electrode 5 via oil 6 . Due to the change in insulation resistance based on the amount of oil 6, the DC voltage at one electrode 5 changes. A DC voltage based on a change in the amount of oil 6 is applied to one input terminal (inverting input terminal) of an operational amplifier 1 connected to a connection point between a resistor 4 of 1 GΩ or more and one electrode 5, and a resistor 2,
A reference voltage is applied to the other input terminal (non-inverting input terminal) of the operational amplifier 1 connected to the connection point of 3, and one input terminal (inverting input terminal) and the other input terminal (non-inverting input terminal) The potential difference between the two is detected at the output terminal of the operational amplifier 1 as an output change.

Embodiment Hereinafter, embodiments of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, reference number 7 indicates the wall of the container, which is connected to the same potential as the installation line. Reference numbers 2 and 3 are first and second resistors connected in series between the DC power supply and the installation line for dividing the DC power supply voltage to obtain a reference voltage. Reference number 4 is a third resistor connected between the power source and one positive electrode 5 and having a resistance value of 1 GΩ or more. The space between the liquid level detection electrode 5 as one electrode on the positive side and the ground electrode 8 as the other electrode on the negative side is filled with oil 6 to be detected housed in a container 9 having a wall 7 . The liquid level detection electrode 5 and the ground electrode 8 constitute an oil level sensor. The liquid level detection electrode 5 and the ground electrode 8 are, for example, a pair of coaxially arranged cylindrical tubes (not shown) or an electrode used as a liquid level detection electrode and a conductive container 9 used as a ground electrode. configured. Reference number 1 is an operational amplifier in which one input terminal is the inverting input terminal.
The non-inverting input terminal as the other input terminal is connected to the connection point between the first resistor 2 and the second resistor 3. The operational amplifier 1 generates an output voltage at the output terminal based on the potential difference between the input terminals.
In the illustrated example, a voltage is generated at the output terminal based on a change in insulation resistance between the liquid level detection electrode 5 and the ground electrode 8.

Figure 2 shows the voltage at the inverting input terminal of operational amplifier 1.
It is a graph showing Va. Curves of the voltage at the inverting input terminal of the operational amplifier 1 due to temperature changes are shown at c and d. The reference value of the DC voltage Va is set to, for example, 9V, and the reference value of the output voltage of the operational amplifier 1 is appropriately set by the potential divided by the first resistor 2 and the second resistor 3. In the output voltage curve in Figure 2, c indicates the relationship between temperature and input voltage when high insulating oil is used as the detected oil, and d indicates the relationship between temperature and input voltage when low insulating oil is used as the detected oil. It shows the relationship of input voltage.

As described above, since the present invention uses a DC power source as an input signal source, it is easy to obtain a stable detection level, and precise and stable detection of minute changes in oil level is possible. Of course, a car battery can also be used as a DC power source. Furthermore, since the current flowing through each resistor and oil is extremely small, power consumption is low.

Also, the insulation resistance of oil is approximately 100GΩ ~
Since it is approximately 500GΩ, the DC power supply voltage can be divided in a well-balanced manner by connecting a resistor having a resistance value of 1GΩ or more between the DC power supply and the liquid level detection electrode. Therefore, minute changes in current due to changes in insulation resistance between the liquid level detection electrode and the ground electrode can be detected sensitively and reliably.

FIG. 3 is a circuit diagram of another embodiment of the present invention.

The circuit shown in Figure 3 differs from the circuit shown in Figure 1 in that it is provided with a thermistor 10. The thermistor 10 is provided to change the reference voltage supplied to the non-inverting input terminal of the operational amplifier 1 in accordance with temperature changes, and either a positive or negative thermistor can be used depending on the position at which it is inserted.
That is, since the insulation resistance of the oil decreases as the temperature rises, when it is inserted on the second resistor 3 side,
Resistance value decreases with increasing temperature (negative characteristic)
When inserted into the first resistor 2, a resistor whose resistance value increases with increasing temperature (positive characteristic) is used.

FIG. 4 is a graph showing the characteristics of the connection potential between the third resistor 4 and the liquid level detection electrode 5. In the figure, e
is a region where the potential changes when there is nothing between the liquid level detection electrode 5 and the ground electrode 8, that is, when the electrode is filled with air. Also, f is the liquid level detection electrode 5
This is a region where the potential changes when oil is filled between the ground electrode 8 and the ground electrode 8. That is, in the device according to the present invention, the first resistor 2 and the second resistor 3
Since regions e and f can be prevented from overlapping with respect to the connection potential Vr between them, stable detection can be achieved over a wide range of temperature changes and types of oil.

In the above embodiment, the positive power supply voltage is applied to the liquid level detection electrode 5, but it is also possible to apply a negative power supply voltage to the liquid level detection electrode 5 by grounding the + side of the power supply. It is also possible to configure

Effects of the invention As described above, the present invention sensitively and reliably detects minute changes in current based on changes in insulation resistance between the liquid level detection electrode and the ground electrode, making it possible to detect minute changes in oil level. can be performed precisely and stably. Further, according to the present invention, a detection circuit for an oil level sensor can be obtained which has an easy circuit configuration and can be used even in extremely cold regions.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of an embodiment of the present invention, Figure 2 is a graph showing the voltage Va at the inverting input terminal of operational amplifier 1, Figure 3 is a circuit diagram of another embodiment of the present invention, and Figure 4 is a graph showing the voltage Va at the inverting input terminal of operational amplifier 1.
The figure is a graph showing the characteristics of the potential at the connection point between the resistor 4 and the liquid level detection electrode 5, FIG. 5 is a graph showing the relationship between temperature and insulation resistance, and FIG. 6 is a circuit diagram of a conventional example. 1... operational amplifier, 2... first resistor, 3...
...Second resistor, 4...Third resistor, 5...Liquid level detection electrode, 6...Oil, 8...Grounding electrode, 1
0...Thermistor.

Claims (1)

[Claims for Utility Model Registration] (1) First and second resistors connected in series to a DC power supply and dividing the DC power supply voltage, and a resistance value of 1GΩ (gigaohm) or more connected to the DC power supply. a third resistor having: one electrode connected in series to the third resistor; the other electrode disposed so as to be energized through oil to the one electrode; one input terminal connected to the connection point of the resistor and the one electrode, and the other input terminal connected to the connection point of the first and second resistors; A DC power supply voltage divided by a resistor is input as a reference voltage to the other input terminal, and a fluctuating voltage based on a change in insulation resistance between the other electrode and the one electrode is input to the one input terminal. 1. A detection circuit for an oil level sensor, comprising: an operational amplifier that is input to a terminal and produces an output voltage that changes depending on a change in potential difference between the other input terminal and the one input terminal. (2) The oil level sensor according to claim 1, wherein a thermistor is connected in series to at least one of the first and second resistors to correct fluctuations in the detected voltage due to temperature changes. detection circuit.