JPH07139988A - Liquid level detector - Google Patents

Abstract

PURPOSE:To constantly prevent erroneous detection caused by the fluctuation/ behavior of a liquid level by providing at least one portion of a thermistor at the lower part of a reference liquid level. CONSTITUTION:Since a reference liquid level BL is provided above the lowest point of a thermistor 22, no conduction is made to light up a warning lamp until an atmospheric temperature around a thermistor 2 reaches a specific value even if a read switch 21 is turned on by mistake. At the atmospheric temperature where the thermistor 22 lights up the lamp, oil increase is eliminated by the temperature so that a float 35 takes a position according to the normal amount of oil before the thermistor 22 energizes the circuit, the read switch 21 is normally operated and is turned off, and the lamp is not lit even if oil increase is generated. The thermistor 22 shows a large resistance at a temperature region where oil increase is generated, thus avoiding the energization of the circuit and preventing erroneous detection due to oil increase.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid level detecting device used for detecting a change in the liquid level of an oil pan of an internal combustion engine or the like.

[0002]

2. Description of the Related Art Conventionally, as this type of technology, for example, "Toyota Crown Majesta New Model Car Manual (1991 1
The engine oil level sensor and the oil level warning system using the same are known.

The oil level sensor introduced here is
It is attached to an oil pan and consists of a thermo switch that is turned on and off by moving the float up and down. Then, as a warning system, when the oil level decreases below a predetermined reference liquid level, the oil level sensor detects it. Further, in response to the detection signal, a dedicated electronic control circuit (ECU circuit) drives the display in the combination meter to display. As a result, the driver is warned that the oil in the oil pan is insufficient.

Generally, in an oil pan, when the oil temperature is lower than a predetermined value, the oil viscosity rises to the engine due to the high oil viscosity, and the oil level may drop even though the engine oil amount is sufficient. Are known. Therefore, in the above oil level sensor, when the oil temperature is lower than a predetermined value, the thermo switch is turned off, and the ECU circuit receives it and causes the display to display an oil shortage regardless of whether the reed switch is on or off. There is no such thing. On the other hand, if the oil temperature drops above the specified level and the oil amount drops below the specified level,
Both the thermo switch and the reed switch are turned on, and the ECU circuit receives the signal and causes the display to display an oil shortage. Further, during cornering of a traveling vehicle, traveling on an inclined surface, etc., there is a possibility that the oil level sensor may erroneously detect due to fluctuations and behavior of the oil liquid level. Therefore, this oil level warning system is provided with a delay circuit for delaying the switching of the on / off signal from the reed switch for a predetermined time (about 40 seconds). The delay circuit delays the display of the oil shortage on the display executed by the ECU circuit.

On the other hand, in the liquid level detection device (Japanese Patent Application No. 05-110741) filed earlier by the same applicant,
Since the delay circuit in the oil level warning system is complicated and expensive, when the oil temperature at the time of engine start is a low temperature below a predetermined value, power is not supplied and when the oil temperature exceeds a predetermined value. There is disclosed a thermoswitch in which an NTC thermistor (hereinafter referred to as a thermistor) having a characteristic of conducting electricity at an ambient temperature (about 60 ° C. or higher) is disclosed. As a result, it is possible to prevent erroneous detection of the liquid level in the oil pan caused by oil rising at the time of engine start without providing a delay circuit. Therefore, when the oil temperature becomes higher than a predetermined value after the engine is started, the above oil rise is eliminated, and when the reed switch is in the on / off operation at the normal prescribed liquid level, the thermistor is energized. It is in a state where it is possible to display an appropriate oil shortage.

[0006]

However, in such a device, as a characteristic of the thermistor, when a voltage is applied at a temperature higher than a predetermined ambient temperature, the thermistor generates heat due to its resistance when energized, and the temperature is high. Become. Since this thermistor uses an NTC thermistor whose resistance value becomes smaller as the temperature itself becomes higher, if the temperature rises due to heat generation due to energization and the temperature becomes high, the resistance value becomes smaller accordingly and more current is supplied to the circuit. Will be accepted. A thermistor having such energization characteristics (hereinafter referred to as thermal runaway) has an atmospheric temperature at an oil temperature (a predetermined value, about 60 ° C) at which a normal oil reference liquid level is detected unless a means for suppressing the heat generation is provided. In the above, when a voltage is applied to this thermistor, thermal runaway occurs and a large amount of electricity is allowed to pass in a short time.

Therefore, when the oil is in the vicinity of the reference liquid level, the liquid level fluctuates due to the inclination of the vehicle, etc., and when the reed switch is turned on and a voltage is applied to the thermistor, the thermistor becomes large in the circuit in a short time. Allow the amount of electricity and display the oil shortage on the display. Therefore, when the ambient temperature around the thermistor at the oil temperature at engine start is below a predetermined value (60 ° C or less), the driver will not be erroneously indicated that the oil is insufficient due to the characteristics of the thermistor. If the ambient temperature around the thermistor is higher than a predetermined value (60 ° C or higher) due to the oil temperature during the operation of, the erroneous detection display of oil shortage due to the fluctuation and behavior of the oil level is frequently displayed. There is a fear that a so-called chattering phenomenon will occur.

In view of the above-mentioned problems, the present invention absorbs the heat of the thermistor to suppress thermal runaway of the thermistor, so that erroneous detection due to fluctuations and behavior of the liquid level can be achieved without providing a special delay circuit. It is an object of the present invention to provide a liquid level detecting device capable of constantly preventing the above.

[0009]

In order to achieve the above object, the gist of the present invention resides in the liquid level detecting device according to the first aspect of the present invention, in which the liquid level is predetermined in the liquid reservoir. A switch that is turned on when the reference liquid level becomes lower than the reference liquid level, and a thermistor that is arranged in the liquid reservoir and has a resistance value that decreases after a predetermined time corresponding to the ambient temperature has passed after a voltage is applied. At least a part of the thermistor is installed below the reference liquid level in the liquid reservoir. Further, in the liquid level detecting device according to the second aspect of the present invention, the thermistor is arranged in the liquid reservoir, and the resistance value becomes low after a predetermined time corresponding to the ambient temperature has passed since the voltage was applied. In the provided liquid level detecting device, at least a part of the thermistor is installed below a reference liquid level to be sensed in the liquid reservoir.

[0010]

According to the liquid level detecting device of the first aspect of the present invention, at least a part of the thermistor is located in the liquid reservoir below the reference liquid level in the liquid level detecting device of the first aspect. Is installed, and a switch that turns on when the liquid level falls below a predetermined reference liquid level is used for setting, so that the liquid level is near the predetermined reference liquid level and Even if the thermistor is energized due to fluctuations / behaviors that are temporarily turned on, the thermistors do not energize the circuit when the ambient temperature is low, and fluctuations / behaviors occur in the liquid level. Then, the switch is temporarily turned on to energize the thermistor, and when the ambient temperature with respect to the thermistor is above a specified value (about 60 ° C or more), the thermistor is high enough to run hot. And becomes even, for bathing at least partially in the liquid, the heat liquid is absorbed, the thermistor is not a high temperature enough to thermal runaway. That is,
Since the heat is radiated to the liquid to some extent, thermal runaway of the thermistor can be suppressed.

According to the liquid level detecting device of the second aspect of the present invention, the above-mentioned first aspect is provided in the liquid reservoir.
Since at least a part of the thermistor is installed below the reference liquid level in the liquid level detection device described, the voltage is constantly applied to the thermistor, and when the liquid level is near the predetermined reference liquid level, the liquid temperature Even if the temperature of the thermistor that is constantly energized becomes a predetermined value or higher (about 60 ° C or higher) and the thermistor becomes hot enough to run out of heat, at least part of it must be immersed in the liquid. Since the liquid absorbs the heat, the thermistor does not reach a temperature high enough to cause thermal runaway. That is, since the heat generated by the thermistor is radiated into the liquid to some extent, thermal runaway of the thermistor can be suppressed.

[0012]

First Embodiment An example in which the liquid level detecting device according to the first embodiment of the present invention is embodied as an automobile oil level detecting device will be described in detail below with reference to FIGS.

FIG. 2 is an electric circuit diagram showing the construction of the liquid level detecting device in this embodiment. This liquid level detection device includes a reed switch 21 and an NTC thermistor 22.
And a warning lamp 23, which constitutes a warning means, are connected in series with each other to form a series circuit.
One end of the series circuit is connected to the positive terminal (B +) of the battery and the other end is grounded (GND).

The reed switch 21 is a float 3 which will be described later.
It is activated by the vertical movement of 5, and when it is turned on, it becomes possible to energize. Further, the resistance value of the thermistor 22 becomes low after a lapse of a predetermined time corresponding to the ambient temperature after the voltage is applied, whereby the energization is allowed. That is, the switching operation is reached.

The characteristics of the reed switch 21 used in this embodiment will be described with reference to FIGS. This is to prevent the reed switch 21 from repeatedly turning on and off due to the fluctuation of the oil level, that is, the strength of the magnetic field received from the magnet 37 when the reed switch 21 switches from the off state to the on state. Is set as a moving value Pi, and conversely, the strength of the magnetic field at the time of switching from the on state to the off state is set as an open value Do. In this embodiment, the ratio (Do / Pi) between the open value Do and the emotional value Pi is "0.
2 to 0.6 ”. Further, due to the difference in the moving range and the moving direction of the magnet 37 with respect to the reed switch 21, the reed switch 21 is switched on and off with some hysteresis. In this embodiment, the hysteresis is defined as a “hold area”, and the “hold area” is “0.5 to 4.0 mm”.
Is set in the range. That is, the open value Do and the moving value P
The relationship between the "hold area" and the ratio (Do / Pi) to i is set so as to fall within the range indicated by the diagonal lines in the graph of FIG.

More specifically, in FIGS. 4 (a) and 4 (b), the reed switch 21 is turned on / off under the influence of the magnetic field of the magnet 37 which can move up and down around it. That is, as shown in FIG.
In a state in which 7 is separated from the contact 21c of the reed switch 21 to some extent, the contact 21c is opened and the reed switch 2
1 is turned off. In addition, as shown in FIG.
When the magnet 37 approaches the contact 21c of the reed switch 21 to some extent, the contact 21c is closed and the reed switch 21 is turned on. Once the reed switch 21 is turned on, the contact 21c retains the closing force, which makes it difficult to open the contact 21c. Therefore, as shown in FIG. 5, even if the magnet 37 moves to some extent, the reed switch 21 is kept in the ON state within the range affected by the magnetic field. Also,
As shown in FIG. 5, the moving range of the magnet 37 in which the ON state of the reed switch 21 is held is slightly different due to the difference in the moving direction (the direction of the solid arrow and the direction of the broken arrow), and there is a deviation of the moving range. Is the “hold area”. This "hold area" is determined depending on the open value Do, the moving value Pi, and the like. In this embodiment, the open value Do and the impression value Pi are determined by appropriately changing the material and rigidity of the contact 21c of the reed switch 21. In addition, the ratio of the open value Do and the emotional value Pi (Do
/ Pi) and the magnetized state of the magnet 37, etc., the "hold area" is determined. Further, in this embodiment, the moving range of the magnet 37, that is, the position of the "hold area" between the uppermost position and the lowermost position is set to have a relationship as shown in FIG.

Next, the characteristics of the thermistor 22 will be described in detail. The graph of FIG. 6 shows the relationship between the terminal voltage and the energization current of the thermistor 22, which is experimentally confirmed under a certain ambient temperature. As can be seen from this graph, the inter-terminal voltage increases as the energizing current increases, but the increase reaches a peak at a certain current value I1, and further gradually decreases from the current value I2. This is because the thermistor 22 itself generates heat and causes thermal runaway when the increase in the energizing current exceeds the current value I1, causing the resistance value to gradually decrease.

The graph of FIG. 7 shows the relationship of the resistance value with respect to the ambient temperature of the thermistor 22 experimentally confirmed under a certain constant current value ("0.1 mA", "100 mA"). As you can see from this graph,
When a current of only “0.1 mA” is applied (that is, in a substantially non-conducting state), the resistance value gradually decreases as the ambient temperature rises to around “350 ° C.” and the temperature is measured. It shows suitable characteristics for. In contrast, "10
When a current of "0 mA" is applied (a substantially normal energized state), the resistance value is drastically reduced at the ambient temperature of "60 ° C". This is because the increase in the ambient temperature is almost 60 °.
When the temperature reaches “C”, the thermistor 22 itself rapidly generates heat and causes thermal runaway.

The graph of FIG. 8 shows that a certain voltage ("12
V ”,“ 15V ”), the relationship between the delay time of the switching operation and the ambient temperature of the thermistor 22, which has been experimentally confirmed, is shown. As can be seen from this graph, the delay time becomes shorter as the ambient temperature rises. Here, for example, at an ambient temperature of “100 ° C.”, it is almost “55” with respect to the voltages of “12V” and “15V”.
Delay times of "second" and "40 seconds" are obtained.

As described above, in this embodiment, the above-mentioned sensor circuit 24 is constituted by the thermistor 22 and the reed switch 21 having the above characteristics.

On the other hand, the warning lamp 23 is arranged in a combination meter in the driver's seat (not shown). The warning lamp 23 is turned on when a current larger than a predetermined value is supplied through the reed switch 21 and the thermistor 22, thereby warning the driver of the oil shortage.

Next, the configuration of this embodiment is shown in FIG.
FIG. 1 is a sectional view showing the structure of an oil level sensor 25 according to the present invention. The oil level sensor 25 includes a terminal housing 26 made of a conductive metal, and a connector 27 made of an insulating material is assembled on the upper side of the housing 26. A terminal 27a is provided inside the connector 27, and the terminal 27a is connected to a battery (not shown) via the warning lamp 23 described above. A bracket 28 made of a conductive metal is attached to the lower side of the terminal housing 26. The bracket 28 has an L-shaped cross section, and the tip end side thereof is an arm 29 extending horizontally. A cover 30 made of an insulating material is attached to the upper surface of the arm 29. Also, the cover 30
Terminals 31 and 32 having two blades are attached to the upper surface of the.

On the other hand, a protective pipe 33 extending downward is integrally provided on the lower surface side of the cover 30. The protection pipe 33 is arranged so as to pass through the arm 29, and is opened downward. A plurality of holes 33a for venting air are formed at the base of the protection pipe 33. The above-mentioned thermistor 22 is fixed to the cover 30 and arranged inside the protective pipe 33. In addition, a pair of lead wires 22 extending from the thermistor 22.
a and 22b are connected to the terminals 31 and 32, respectively.

Similarly, another protective pipe 34 extending downward is attached to the lower surface side of the cover 30. The protection pipe 34 is made of a conductive metal, penetrates the arm 29, and is arranged below the arm 29. The reed switch 21 is arranged inside the protection pipe 34. That is, the protection pipe 34 is arranged in parallel with the protection pipe 33 in the same horizontal plane, and the reed switch 21 therein is also arranged in parallel with the thermistor 22 in substantially the same horizontal plane. A ring-shaped float 35 is attached to the outer periphery of the protection pipe 34 so as to be vertically movable. A stopper 36, which is larger in diameter than the pipe 34 and is made of conductive metal, is fixed to the lower side of the protection pipe. This stopper 36 allows the float 35
It is protected from slipping out. Inside the float 35,
Magnet 37 for operating the reed switch 21
Is built in. Further, one lead wire 21 a of the reed switch 21 penetrates the cover 30 and is connected to the terminal 3
2 and the other lead wire 21b is connected to the stopper 36.
Is connected to and grounded.

Then, the terminal 27a of the connector 27
And a terminal 31 on the cover 30 are connected by a lead wire 38. In this way, terminal 27
The reed switch 21 and the thermistor 22 are electrically connected in series between a and the bracket 28. The oil level sensor 25 configured as described above is attached to the engine block 39 by the terminal housing 26 thereof. And the two protection pipes 33,
34 is immersed in the engine oil of an oil pan 40 as an oil reservoir.

In this embodiment, the reed switch 21
The positional relationship between and the thermistor 22 is set as follows. That is, as shown in FIGS. 9 and 1, when the position where the reed switch 21 is turned on by the float 35 described above is the reference liquid level BL, the thermistor 22 is partially disposed below the reference liquid level BL. Has been done. Specifically, the reference liquid level BL and the thermistor 2
The relative height H with respect to 2 is set to "-2 mm".

The operation of the oil level OL and reed switch 21 having the above-described structure and the thermistor 22 in the liquid level detecting apparatus of this embodiment will be described below. In FIG. 1, when the engine oil amount is sufficient,
The float 35 located in the engine oil hits the arm 29 in an attempt to float and is located above the protection pipe 34. As a result, the reed switch 21
Is turned off and the circuit is not energized.

Now, in FIG. 10 and FIG. 1, when the engine oil amount is sufficient and the oil level OL is sufficiently high,
Since the float 35 located in the engine oil is located above the protection pipe 34, the reed switch 21 is always off. Therefore, no current flows from the battery (not shown) to the thermistor 22 and the warning lamp 23. Since the thermistor 22 is in the non-energized state, its resistance value changes only slightly as the ambient temperature rises. Of course, since the circuit is not energized, the warning lamp 23 remains off.

On the other hand, when the engine oil amount decreases and the oil level OL becomes lower than the predetermined reference liquid level BL, the float 35 located in the engine oil is protected by the protective pipe as the level decreases. It will be located at the bottom of 34. As a result, the reed switch 2
1 is turned on by the magnetic force of the magnet 37 and is in an energized state. Therefore, at the same time when the reed switch 21 is turned on, a voltage is applied to the thermistor 22 from the battery.

FIG. 11 schematically shows the allowable energization amount of the thermistor 22 at this time as a lighting mode of the warning lamp together with its resistance value. Thermistor 22 at this time
Generates heat after applying a voltage with a resistance value according to the ambient temperature at that time. However, when the reed switch 21 is turned on, a part of the thermistor 22 is below the oil level OL as described above, that is, because it is immersed in the liquid, the heat is radiated into the oil liquid. . Therefore, the amount of heat that the thermistor 22 has is adjusted from the relationship between heat generation and heat dissipation according to the ratio of the immersion liquid, and the thermistor 22 is eventually
Energizes the circuit by the resistance value according to the heat that can be held at that time. That is, in FIG. 11, the thermistor 22 generates heat from the time when the ambient temperature rises and exceeds 60 ° C.
Although the resistance value is lowered and electricity is applied, since the oil absorbs the heat of the thermistor 22 at this time, the thermistor 22
The amount of heat that can have is fixed. Therefore, the thermistor 22 shows the resistance value in the amount of heat at this time. With respect to the resistance value (10Ω in the drawing) of the thermistor 22 in such a state, the current supplied to the circuit is a current that causes the warning lamp 23 to light up in a dark state.

After that, as the oil level OL in the oil pan decreases, the rate of heat radiation of the thermistor 22 decreases (that is, the rate of oil that absorbs the heat of the thermistor 22 decreases). The amount of heat that can be held increases. Therefore, the resistance value correspondingly decreases, and a larger amount of electricity is supplied from the amount of electricity that the thermistor 22 allows. That is, FIG.
As shown in, the oil level OL decreases and the entire thermistor 22 is positioned above the oil level OL,
When the generated heat can no longer be dissipated (when it is no longer absorbed), the thermistor 22 generates heat due to the ambient temperature, and its resistance value becomes extremely low, causing thermal runaway. Therefore, the current supplied to the circuit with respect to the resistance value (1Ω in the drawing) of the thermistor 22 at this time is a current that causes the warning lamp 23 to light up brightly.

As described above, since a part of the thermistor 22 is arranged below the reference liquid level BL and the thermistor 22 is immersed in the oil, the heat generated is absorbed by the oil, and the thermistor 22 is thermally runaway. There is nothing to do.

Second Embodiment Next, a liquid level detecting device according to a second embodiment of the present invention will be described.

The structure of the liquid level detecting device in the second embodiment is basically the same as that shown in the first embodiment. Further, in this embodiment, the relative height H between the thermistor 22 and the reference liquid level BL set in the first embodiment is set from "-2 mm" to "-5" as shown in FIG.
mm ”, the lighting amount of the warning lamp 23 with respect to the reference liquid level BL is adjusted.

Therefore, the operation of the second embodiment will be described by comparing the lighting mode of the warning lamp 23 with that of the first embodiment. As shown in FIG. 13, the relative height H between the thermistor 22 and the reference liquid level BL is “−5 m.
In the present embodiment set by "m", even if the oil level OL becomes equal to or lower than the reference liquid level BL, all of the thermistor 22 is in a state of being immersed in the oil. Therefore, the thermistor 22 is energized by the ON state of the reed switch 21 in that state, and generates heat according to the ambient temperature around the thermistor 22 at that time. However, since the entire thermistor 22 is immersed in the oil, when the heat that can be generated and the heat that can be held is almost absorbed by the oil, the resistance value does not decrease significantly because thermal runaway does not occur. Therefore, even if the circuit is energized, the energization amount is not enough to turn on the warning lamp 23.

As described above, since all of the thermistor 22 is arranged below the reference liquid level BL and the thermistor 22 is submerged in the oil, the heat generated is absorbed by the oil, and the thermistor 22 causes thermal runaway. There is no such thing.

As in the first and second embodiments, the resistance value of the thermistor 22 and the amount of electricity supplied to the circuit (that is, the amount of lighting of the warning lamp) are determined by the thermistor 22.
Height of the oil level OL and the thermistor 2
It depends on the timing of voltage application to the 2nd circuit.

Therefore, FIG. 14 shows the relationship between the reference liquid level BL, the relative height H between the lower end of the thermistor 22, the average current flowing through the thermistor 22 and the average delay time of the thermistor 22. This graph shows the energization mode of the thermistor 22 when the ambient temperature is about 60 ° C or higher.

In this graph, the curve A shown by the solid line,
“A” shows an experimental result under the condition that the vibration wave height of the oil surface is “1 mm or less”. Curve B shown by a two-dot chain line,
b shows the experimental result under the condition that the vibration wave height of the oil surface is “3 mm” and the vibration frequency is “0.3 Hz”. Also, the curved lines C and c indicated by broken lines have the vibration wave height of the oil level of "3 mm" and the vibration frequency of "0.1 Hz".
It shows the experimental results under the condition. Further, in this graph, a region above the reference current value Ib indicates a “lighting region” in which the warning lamp 23 can be lit, and a region above the reference time Tb is a “practical use” that satisfies a practical delay time. Area ”. Further, the position where the relative height H is “0” is the reference liquid level BL, the lower side of the reference liquid level BL is “in the liquid”, and the upper side is “in the air”.

In the liquid level detecting device of the present invention, at least a part of the thermistor 22 is installed below the reference liquid level BL, so that the position of the reference liquid level BL indicated by the alternate long and short dash line in FIG. H of the relative height of the figure
Will be negative. In that region, the energization amount Ib that the thermistor 22 can allow in the circuit changes from the extinguishing current of the warning lamp 23 to the lighting current (dark) and then to the lighting current (bright).

The reed switch 21 shown in the first embodiment.
When the relative height H between the thermistor 22 and the thermistor 22 is "-2 mm", the reed switch 21 energizes the thermistor 22 at the timing shown by the chain double-dashed line. Thermistor 22 at this time
The current Ib allowed by the circuit is the warning lamp 23
Is a lighting current (dark) such that the lamp lights darkly. Later,
As the oil decreases, the circuit is energized with a lighting current (bright) that brightens the warning lamp 23.

Further, the relative height H between the reed switch 21 and the thermistor 22 shown in the second embodiment is "-5 mm".
In the case of, the reed switch 2 at the timing shown by the dashed line
1 energizes the thermistor 22. The current Ib allowed in the circuit by the thermistor 22 at this time is an extinguishing current such that the warning lamp 23 is not yet turned on. Therefore, thereafter, as the oil decreases, the circuit is energized from a lighting current (dark) at which the warning lamp 23 is lit darkly to a lighting current (bright) at which the warning lamp 23 is brightly lit.

Also, in the conditions shown by the curves A and a in the figure, a sufficient delay time is set until the current flows to the thermistor for lighting the warning lamp 23.

FIG. 15 shows a conventional oil level OL of the liquid level detecting device constituted by the first or second device as described above, the current flowing through the thermistor 22 at that time, and the current flowing through the entire circuit. Thermistor 22
Position setting (H ≧ 0) and the thermistor 22 in the present invention
The data which compared the effect | action with the position setting (H <0) of are shown. FIG. 15 is a schematic representation of an actual vehicle on the assumption that its oil level OL fluctuates due to its vibrations. For simplicity, the oil level OL is 3 with respect to the reference liquid level BL. It shows how the standard level decreases below that level. Figure 15
FIG. 15A shows a mode of current flowing through the thermistor 22 in the present invention, and FIG. 15B shows a mode of current flowing through the thermistor 22 in the conventional device.

The thermistor 2 as shown in FIG.
In the conventional case where 2 is set above the reference liquid level BL, when the oil level OL fluctuates in the vicinity of the reference liquid level BL, the reed switch 21 is repeatedly turned on and off each time, so that the reed switch 21 is When it is turned on and the thermistor 22 is energized at that time, the thermistor 22 causes thermal runaway due to the ambient temperature at that time, and a lighting current (bright) is energized all at once to the circuit. That is, a chattering phenomenon that causes the warning lamp 23 to light up on the display is caused. Then, when the oil level OL becomes equal to or lower than the reference liquid level, the reed switch 21 is always turned on, so that the thermistor 22 always supplies a substantially constant lighting current (bright) to the display due to thermal runaway. The warning lamp 23 is turned on.

However, in the embodiment of the present invention, as shown in FIG.
As shown in 5 (a), the oil level OL fluctuates in the vicinity of the reference liquid level BL, the reed switch 21 repeatedly turns on and off each time, and the thermistor 22 is energized when the reed switch 21 is turned on. As a result, even if the heat is generated at a high temperature, at least a part of the heat is absorbed in the oil, and the heat is absorbed by the oil.
Therefore, at this oil level OL, the thermistor 22
Even if the circuit is energized for a time exceeding the delay time, the circuit is not allowed to energize so as to become a lighting current due to thermal runaway. That is, even if the reed switch 21 is turned on and the thermistor 22 is energized, the current that the thermistor 22 energizes the circuit is in the range of the extinguishing current of the warning lamp 23 at most.

Next, when the oil level OL becomes lower than the reference liquid level BL, the reed switch 21 is always turned on. However, even if the thermistor 22 is energized, for example, half of the thermistor 22 is Since the liquid is immersed in the oil, the amount of heat generated by the heat is absorbed by the oil, and thermal runaway does not allow the circuit to be energized to a lighting current (bright). However, since the ratio of the immersion liquid into the oil of the thermistor 22 is small, the heat radiation into the oil of the thermistor 22 is correspondingly small. This will somewhat increase the amount of current that the thermistor 22 will allow to the circuit. That is, the energizing amount at this time is the warning lamp 2
3 is a darkly illuminated area.

The next stage shows the case where the oil level OL is further reduced and the oil needs to be replenished. When the thermistor 22 is exposed from the oil level OL and comes to be positioned above so that the heat generated by the thermistor 22 is no longer absorbed, as described above,
2 becomes thermal runaway, and the lighting current (bright), which is a region where the warning lamp 23 is brightly lit, is applied to the circuit.

As an effect of the above first and second embodiments, the reference liquid level BL is set to a position above the lowest point of the thermistor 22, so that, for example, when the engine is cold, oil rises. Even if the reed switch 21 is turned on by mistake, the thermistor 22 will not emit a warning lamp until the ambient temperature around the thermistor 22 reaches a predetermined value (about 60 ° C.) in the state shown in FIG. Do not energize to turn on 23.
Then, at the ambient temperature around the thermistor 22 (that is, at the time when the oil temperature rises) where the thermistor 22 conducts electricity for radiating heat into the liquid, that is, for turning on the warning lamp 23, the oil rises. Because it is no longer solved by that temperature,
Before the thermistor 22 applies a current to the circuit (to the extent that the warning lamp is dimly lit), the float 35 takes a normal oil position, and the reed switch 21 operates normally to turn off. Therefore, no matter how much oil rises, the warning lamp 23 will not be turned on.

As described above, in the erroneous detection due to oil rising, the thermistor 22 has a large resistance value (1000Ω) in the temperature range where oil rising is caused, so that the circuit is not energized. Therefore, when the thermistor 22 is energized in a large amount, it is limited to the case where the oil level OL is sufficiently lower than the reference liquid level BL.

[0050]

Third Embodiment An example in which the liquid level detecting device according to the third embodiment of the present invention is embodied as an automobile oil level detecting device will be described in detail with reference to FIGS.

FIG. 16 is an electric circuit diagram showing the construction of the liquid level detecting device in this embodiment. This liquid level detection device includes a reed switch 21 and an NTC thermistor 22.
And a warning lamp 23, which constitutes a warning means, are connected in series with each other to form a series circuit.
One end of the series circuit is connected to the positive terminal (B +) of the battery and the other end is grounded (GND).

On the other hand, the warning lamp 23 is arranged in a combination meter (not shown) in the driver's seat. The warning lamp 23 is connected to the thermistor 22.
It lights up according to the current supplied through it, which alerts the driver of the lack of oil.

Next, FIG. 17 shows the configuration of the present embodiment. FIG. 17 is a sectional view showing the structure of the oil level sensor 25 according to the present invention. This oil level sensor 25
Is provided with a terminal housing 26 made of a conductive metal, and a connector 27 made of an insulating material is attached to the upper side of the housing 26. A terminal 27a is provided inside the connector 27.
a is connected to a battery (not shown) through the warning lamp 23 described above. Terminal housing 2
A bracket 28 made of a conductive metal is attached to the lower side of 6. The bracket 28 has an L-shaped cross section, and the tip end side of the arm 2 extends horizontally.
It is 9. A cover 30 made of an insulating material is attached to the upper surface of the arm 29. In addition, terminals 31 and 32 having two blades are attached to the upper surface of the cover 30.

On the other hand, a protective pipe 33 extending downward is integrally provided on the lower surface side of the cover 30. The protection pipe 33 is arranged so as to pass through the arm 29, and is opened downward. A plurality of holes 33a for venting air are formed at the base of the protection pipe 33. The above-mentioned thermistor 22 is fixed to the cover 30 and arranged inside the protective pipe 33. In addition, a pair of lead wires 22 extending from the thermistor 22.
a and 22b are connected to the terminals 31 and 32, respectively.

The terminal 27a of the connector 27
And a terminal 31 on the cover 30 are connected by a lead wire 38. In this way, terminal 27
The thermistor 22 is electrically connected in series between a and the bracket 28. The oil level sensor 25 configured as described above is attached to the engine block 39 by the terminal housing 26 thereof. The protection pipe 33 is immersed in the engine oil at the approximate center of the oil pan 40 serving as an oil reservoir.

Further, the position where the protection pipe 33, that is, the thermistor 22 is installed, is selected by arranging the position where the fluctuation of the oil level is considered to be the smallest, depending on the shape of the oil pan.

The positional relationship of the thermistor 22 in this embodiment is set as follows. That is, as shown in FIG. 18, when the position where the amount of oil is judged to be insufficient as described above is the reference liquid level BL, the thermistor 22 is partially disposed below the reference liquid level BL. Specifically, the reference liquid level BL and the thermistor 2
The relative height H with respect to 2 is set to "-3 mm".

Next, the operation of the liquid level detection device in this embodiment using the oil level OL constructed as described above and the thermistor 22 will be described. In FIG. 17 showing the present embodiment, the thermistor 22 is always energized even when the engine oil amount is sufficient.

However, as shown by the dotted line in the third embodiment in FIG. 14, the reference liquid level BL of the thermistor 22.
At a time when the relative height H between the and thermistor 22 is “−3 mm”, even if the thermistor 22 energizes the circuit, the amount of energization that can be tolerated by the thermistor 22 does not turn on the above-mentioned warning lamp 23 but remains off. is there. That is, after the engine is started, the thermistor 22 always energizes the circuit by energization, but the amount of energization at this stage is small and the warning lamp 23 does not light.

When the amount of engine oil gradually decreases and the oil level OL falls below a predetermined reference liquid level BL, the thermistor 22 is positioned above the oil level OL as the level drops. Like

The following is the same as the operation mode of the thermistor 22 after the lead switch 21 is turned on in the first and second embodiments. That is, in the thermistor 22, the oil level OL has a predetermined reference liquid level BL.
If the relative height H of the thermistor 22 with respect to the reference liquid level BL is set to "-3 mm", a part of it is still immersed in the oil (for example, the oil level of the thermistor 22). Relative height H with OL is -2m
Therefore, the heat is radiated into the oil liquid.

As a mode of energizing the thermistor 22 at this time, FIGS. 11 to 12 can be referred to. In the present embodiment, the reed switch does not exist and is always in the energized state. However, in FIGS. 11 and 12, since the energized state to the thermistor 22 is shown, there is a similar action.

That is, in FIG. 11, the thermistor 22 generates heat from the time when the ambient temperature rises and exceeds 60 ° C., and the resistance value is reduced to energize the circuit, but the heat of the thermistor 22 at this time is changed to oil. To absorb some heat,
The amount of heat that the thermistor 22 can have is fixed. Therefore, the thermistor 22 shows the resistance value in the amount of heat at this time.

With respect to the resistance value (10Ω in the drawing) of the thermistor 22 in such a state, the current supplied to the circuit is such a current as causes the warning lamp 23 to light up in the dark.

Thereafter, as the oil level OL in the oil pan further decreases (for example, the relative height H of the thermistor 22 to the oil level OL is -1 mm, 0 mm).
At the point of time), the rate of heat radiation of the thermistor 22 decreases (that is, the rate of oil that absorbs the heat of the thermistor 22 decreases), so the amount of heat that the thermistor 22 can have increases. Therefore, the resistance value correspondingly decreases, and a larger amount of electricity is applied to the circuit from the amount of electricity passed by the thermistor 22 described above.

That is, referring to FIG. 12, as shown here, the oil level OL decreases and the thermistor 22
Is located above the oil level OL, and when the generated heat can no longer be dissipated (is no longer absorbed), the thermistor 22 generates heat due to the ambient temperature.
The resistance value becomes extremely low, causing thermal runaway. Therefore, the current supplied to the circuit with respect to the resistance value (1Ω in the drawing) of the thermistor 22 at this time is a current that causes the warning lamp 23 to light up brightly.

Therefore, as an effect of this embodiment, since the thermistor 22 is partially disposed below the reference liquid level BL and the thermistor 22 is immersed in the oil, the heat generated is absorbed by the oil, and the thermistor is absorbed. 22 does not run out of heat.

Fourth Embodiment Next, a liquid level detecting device according to a fourth embodiment of the present invention will be described with reference to FIGS.

The structure of the liquid level detecting device in the fourth embodiment is basically the same as that shown in the third embodiment. That is, FIG. 19 is an electric circuit diagram showing the configuration of the liquid level detecting device in this embodiment. This liquid level detecting device has a series circuit configuration in which a reed switch 21, an NTC thermistor 22, and a warning lamp 23 constituting a warning means are connected in series to each other. One end of the series circuit is connected to the positive terminal (B +) of the battery and the other end is grounded (GND).

On the other hand, the warning lamp 23 is arranged in the combination meter in the driver's seat (not shown). The warning lamp 23 is connected to the thermistor 22.
It lights up according to the current supplied through it, which alerts the driver of the lack of oil.

Next, FIG. 20 shows the configuration of this embodiment. FIG. 20 is a sectional view showing the structure of the oil level sensor 25 according to the present invention. The oil level sensor 25 includes a terminal housing 26 made of a conductive metal, and a connector 27 made of an insulating material is assembled on the upper side of the housing 26. A terminal 27a is provided inside the connector 27, and the terminal 27a is connected to a battery (not shown) via the warning lamp 23 described above. A bracket 28 made of a conductive metal is attached to the lower side of the terminal housing 26. The bracket 28 has an L-shaped cross section, and the tip end side thereof is an arm 29 extending horizontally. A cover 30 made of an insulating material is attached to the upper surface of the arm 29. Also, the cover 30
Terminals 31 and 32 having two blades are attached to the upper surface of the.

On the other hand, a protective pipe 33 extending downward is integrally provided on the lower surface side of the cover 30. The protection pipe 33 is arranged so as to pass through the arm 29, and is opened downward. A plurality of holes 33a for venting air are formed at the base of the protection pipe 33. The above-mentioned thermistor 22 is fixed to the cover 30 and arranged inside the protective pipe 33. In addition, a pair of lead wires 22 extending from the thermistor 22.
a and 22b are connected to the terminals 31 and 32, respectively.

Then, the terminal 27a of the connector 27
And a terminal 31 on the cover 30 are connected by a lead wire 38. In this way, terminal 27
The thermistor 22 is electrically connected in series between a and the bracket 28. The oil level sensor 25 configured as described above is attached to the engine block 39 by the terminal housing 26 thereof. The protection pipe 33 is immersed in the engine oil at the approximate center of the oil pan 40 serving as an oil reservoir.

Further, the position where the protection pipe 33, that is, the thermistor 22 is installed, is selected by arranging a position where the fluctuation of the oil liquid level is considered to be the smallest, depending on the shape of the oil pan.

The positional relationship of the thermistor 22 in this embodiment is set as follows. That is, as shown in FIG. 21, when the position where the oil amount is determined to be insufficient as described above is the reference liquid level BL, the thermistor 22 is disposed below the reference liquid level BL as a whole. Specifically, the reference liquid level BL and the thermistor 2
The relative height H with respect to 2 is set to "-5 mm".
In this embodiment, the relative height H between the thermistor 22 and the reference liquid level BL set in the third embodiment is set to "-3.
mm "to" -5 mm "and the reference liquid level BL
The lighting amount of the warning lamp 23 and the timing thereof are adjusted.

Next, the operation of the fourth embodiment will be described by comparing the lighting mode of the warning lamp 23 with that of the third embodiment. As shown in FIG. 21, the thermistor 22
In the present embodiment in which the relative height H between the reference liquid level BL and the reference liquid level BL is set to “−5 mm”, even if the oil level OL becomes equal to or lower than the reference liquid level BL, the thermistor 22 is entirely immersed in the oil. It is in the state of doing.

Therefore, the thermistor 22 generates heat according to the ambient temperature around the thermistor 22 at that time while being energized. However, since the entire thermistor 22 is immersed in the oil, when the heat that can be generated and the heat that can be held is almost absorbed by the oil, the resistance value does not decrease significantly because thermal runaway does not occur.
Therefore, even if the circuit is energized, the warning lamp 23
Is not enough to turn on.

As described above, since all of the thermistor 22 is arranged below the reference liquid level BL and the thermistor 22 is immersed in the oil, the heat generation is absorbed by the oil, and the thermistor 22 causes thermal runaway. There is no such thing.

After that, the oil level OL becomes lower as the amount of oil decreases, and after the relative height H with the thermistor 22 becomes "-3 mm", it is the same as the above-mentioned third embodiment. Therefore, the description is omitted.

Further, in the liquid level detecting device comprising only the thermistor 22 as disclosed in the third and fourth embodiments, the warning lamp 23 corresponding to the decrease of the liquid surface position by the shape of the thermistor 22 as shown in the figure. Can be turned on. However, as in the first and second embodiments, the timing of voltage application to the thermistor 22 due to the oil level OL (that is, the timing of warning the driver of the warning lamp 23) is set by a reed switch or the like. If it is desired to take the shape clearly, the shape of the thermistor 22 may be a shape in which the thermistor 22 is laid down sideways as shown in the embodiment of the present invention, or in the lateral direction as shown in FIG. The timing of voltage application to the thermistor 22 can be clearly determined also by using a flat chip shape or a horizontally elongated cylindrical thermistor as shown in FIG.

That is, by using the thermistor having such a shape, it is possible to greatly change the rate at which the thermistor radiates heat to the liquid due to minute fluctuations in the liquid surface. It can be quickly changed to dark) and lighting (bright).

[0081]

As described in detail above, according to the first aspect of the present invention, a voltage is applied when the liquid level becomes equal to or lower than a predetermined reference liquid level in the liquid reservoir, and the voltage is applied. Since a thermistor whose resistance value becomes low after a predetermined time according to the ambient temperature in the liquid reservoir after the addition of is added below the reference liquid level in the liquid reservoir, the warning lamp lights up. When the vehicle is running near the reference liquid level and the current is applied to the thermistor due to the chattering phenomenon caused by the reed switch when the vehicle is running, the heat generated by the thermistor at that point is radiated into the liquid ( That is, since the heat is absorbed by the liquid), the energization amount of this thermistor does not become the energization amount for turning on the warning lamp. Therefore, even if the reed switch causes chattering when the vehicle is running, the warning lamp does not chatter.

According to the second aspect of the present invention, the thermistor whose resistance value becomes lower in the liquid reservoir depending on the ambient temperature in the liquid reservoir is placed below the reference liquid level in the liquid reservoir. Since it is installed, even if the thermistor is energized at all times, the heat generated by the thermistor at this time is absorbed by the liquid in the liquid reservoir, so the amount of electricity energized by the thermistor is very small. That is, there is not enough power to turn on the warning lamp. Therefore, even if the liquid level fluctuates during traveling of the vehicle, the warning lamp does not chatter as long as the liquid level is at least near the reference liquid level.

Further, with such a structure, even when the "oil rise" to the engine at the time of starting the engine of the vehicle is severe, the thermistor may be exposed from the liquid. When the ambient temperature is such that "oil rises" when the engine is started, the amount of electricity supplied to the circuit by the thermistor is so small that the warning lamp is not turned on.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing the overall structure of a liquid level detection device according to a first embodiment of the present invention.

FIG. 2 is an electric circuit diagram showing a configuration of a liquid level detection device according to a first embodiment of the present invention.

FIG. 3 is a graph showing a relationship of a “hold area” with respect to a ratio (Do / Pi) between an open value Do and a moving value Pi in the first embodiment of the present invention.

FIG. 4 is an explanatory diagram for explaining the operation of the reed switch and the positional relationship of the magnets in the first embodiment of the present invention.

FIG. 5 is an explanatory diagram illustrating the relationship between the operation of the reed switch and the “hold area” with respect to the amount of movement of the magnet in the first embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the terminal voltage and the energization current of the thermistor experimentally confirmed under a constant ambient temperature in the first embodiment of the present invention.

FIG. 7 is a graph showing the relationship between the resistance value and the ambient temperature of the thermistor experimentally confirmed under a constant current in the first embodiment of the present invention.

FIG. 8 is a graph showing the relationship between the delay time of the switching operation and the ambient temperature of the thermistor experimentally confirmed under a constant current in the first example of the present invention.

FIG. 9 is a diagram showing the positional relationship between the reference liquid level of the reed switch and the thermistor in the first embodiment of the present invention.

FIG. 10 is a graph showing a relationship between on / off of a reed switch, a resistance value of a thermistor, and lighting / extinguishing of a warning lamp with respect to an ambient temperature when the oil level is high in the first embodiment of the present invention.

FIG. 11 is a graph showing the relationship between the on / off state of the reed switch, the resistance value of the thermistor, and the turning on / off of the warning lamp with respect to the ambient temperature when the oil level decreases to some extent in the first example of the present invention. .

FIG. 12 is a graph showing a first embodiment of the present invention, in which the reed switch is turned on / off and the thermistor resistance is changed with respect to the ambient temperature when the oil level is sufficiently reduced
3 is a graph showing a relationship between lighting and extinguishing of a warning lamp.

FIG. 13 is a diagram showing the positional relationship between the reference liquid level of the reed switch and the thermistor in the second embodiment of the present invention.

FIG. 14 is a graph showing the relationship between the relative height of the reference liquid level and the thermistor, the average current flowing through the thermistor, the lighting amount of the warning lamp, and the average delay time by the thermistor in the example of the present invention. .

FIG. 15 is a measurement diagram showing an operation mode in the comparison between the embodiment of the present invention and the conventional liquid level detecting device.

FIG. 16 is an electric circuit diagram showing the configuration of a liquid level detection device according to a third embodiment of the present invention.

FIG. 17 is a sectional view showing the overall structure of a liquid level detecting device according to a third embodiment of the invention.

FIG. 18 is a diagram showing a positional relationship between a reference liquid level and a thermistor in the third embodiment of the present invention.

FIG. 19 is an electric circuit diagram showing the configuration of a liquid level detection device according to a fourth embodiment of the present invention.

FIG. 20 is a sectional view showing the overall structure of a liquid level detecting device according to a fourth embodiment of the invention.

FIG. 21 is a diagram showing a positional relationship between a reference liquid level and a thermistor in a fourth embodiment of the present invention.

FIG. 22 is a modification of the thermistor according to the liquid level detecting device of the present invention.

[Explanation of symbols]

 OL ・ ・ ・ Oil level (liquid level) BL ・ ・ ・ Reference liquid level 21 ・ ・ ・ Reed switch (switch) 22 ・ ・ ・ Thermistor 40 ・ ・ ・ Oil pan (in the liquid reservoir)

Claims (2)

[Claims] 1. A switch that is turned on when the liquid level in a liquid reservoir falls below a predetermined reference liquid level, and a predetermined time that is arranged in the liquid reservoir and that corresponds to the ambient temperature after a voltage is applied. In a liquid level detecting device comprising a thermistor having a low resistance value after the passage of a liquid level, at least a part of the thermistor is installed below the reference liquid level in the liquid reservoir. Detection device. 2. A liquid level detecting device comprising a thermistor arranged in a liquid reservoir, the resistance value of which decreases after a predetermined time corresponding to an ambient temperature has passed after a voltage is applied, wherein at least one of the thermistors is provided. Part of the liquid level detection device is installed slightly below the reference liquid level sensed in the liquid reservoir.