JPH06317135A - Liquid level detecting device - Google Patents

Abstract

PURPOSE:To prevent false detections resulting from the fluctuation and behavior of a liquid level by omitting any special delay circuit. CONSTITUTION:A reed switch 1, a thermistor 2 and a warning lamp 3 are electrically connected in series to one another. This series circuit is connected to the plus terminal of a battery at one end and grounded at the other end. The reed switch 1 is turned on and off as a float rises and lowers. After a prescribed period of time corresponding to ambient temperature has elapsed from the application of a voltage to the thermistor 2, the resistance value of the thermistor 2 is lowered so that the thermistor 2 is permitted to conduct electricity. When the thermistor 2 is permitted to conduct electricity, the warning lamp 3 is turned on to warn oil shortage. Therefore when the reed switch 1 is turned on as the oil level L is decreased, the thermistor 2 is permitted to conduct electricity after the delay of the prescribed time in compliance with ambient temperature, so that the warning lamp 3 is turned on.

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 kind of technology, for example, an engine oil level sensor introduced in "Toyota Crown Majesta New Model Car Manual (issued in October 1991)" and an oil level warning system using it Are known.

The oil level sensor introduced here is attached to an oil pan and is composed of a reed switch which is turned on and off by the up and down movement of a float and a thermo switch which is turned on and off by the temperature of engine oil. . And as a warning system, when the oil level decreases below a predetermined reference level,
The oil level sensor detects this. 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 of the lack of oil.

Generally, in an oil pan, when the oil temperature is lower than a predetermined value during cold, the oil viscosity is high and oil is likely to rise into the engine. for that reason,
The oil level may drop even though the amount of oil is sufficient. Therefore, in the above oil level sensor, when the oil temperature is low, the thermo switch is turned on, and the ECU circuit receives it and prevents the display of the oil shortage from being displayed regardless of whether the reed switch is on or off. ing. On the other hand, when the oil temperature is above the specified value and the oil level decreases below the reference level while warm, both the thermo switch and the reed switch are turned off, and the ECU circuit receives the indication and displays the oil shortage on the display. It is designed to let you. or,
During cornering of a traveling vehicle, it is possible that the oil level sensor may erroneously detect due to fluctuations and behavior of the oil 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.

[0005]

Therefore, in the above-mentioned prior art, a delay circuit must be separately provided in order to avoid erroneous detection due to fluctuations and behavior of the oil level.
To that extent, the circuit configuration of the entire system becomes complicated, which leads to an increase in cost.

The present invention has been made in view of the above-mentioned circumstances, and a first object thereof is to prevent an erroneous detection due to the fluctuation / behavior of the liquid level by omitting a special delay circuit. It is to provide a possible liquid level detection device. A second object is to provide a liquid level detecting device capable of performing stable detection even when the liquid level frequently changes.

[0007]

In order to achieve the above first object, in the first invention, a switch that is turned on when the liquid level in the liquid reservoir falls below a predetermined reference level, The purpose is to have a thermistor that is placed in the liquid reservoir and has a resistance value that decreases after a lapse of a predetermined time according to the ambient temperature after the voltage is applied, and those switches and the thermistor are electrically connected in series. I am trying.

Further, in order to achieve the above-mentioned second object, in the second invention, a voltage is applied at the same time when the liquid level becomes equal to or lower than a predetermined reference level in the liquid reservoir, and then the voltage is applied. The purpose of the invention is to provide a thermistor whose resistance value decreases after a predetermined time corresponding to the ambient temperature in the liquid reservoir, and to arrange the thermistor near the reference level in the liquid reservoir.

[0009]

According to the first aspect of the invention, when the switch electrically connected in series and the thermistor are connected to the power source, the liquid level in the liquid reservoir becomes equal to or lower than the reference level. The switch is turned on and voltage is applied to the thermistor. In addition, the resistance value of the thermistor becomes low after a predetermined time corresponding to the ambient temperature has passed since the voltage was applied. As a result, the energization of the thermistor is permitted, and the energization is output as an electric signal for instructing the decrease of the liquid level. Therefore, the output of the electric signal for instructing the lowering of the liquid level is delayed only for a predetermined time from when the switch is turned on until the energization of the thermistor is allowed.

Further, according to the structure of the second invention, a voltage is applied to the thermistor at the same time when the liquid level in the liquid reservoir becomes equal to or lower than the reference level. Then, the resistance value of the thermistor becomes low after a lapse of a predetermined time corresponding to the ambient temperature in the liquid reservoir after the voltage is applied. As a result, the energization of the thermistor is permitted, and the energization is output as an electric signal for instructing the decrease of the liquid level. Therefore,
The output of the electric signal instructing the decrease of the liquid level is delayed only for a predetermined time until the energization of the thermistor is allowed. Moreover, since the thermistor is arranged near the reference level, the thermistor is always immersed in the liquid even if the liquid level frequently changes near the reference level. Therefore, the thermistor is constantly deprived of heat by the liquid, and the above-mentioned delay action by the thermistor does not become unstable.

[0011]

【Example】

(First Embodiment) A first embodiment in which the liquid level detecting device of the first invention is embodied as an oil level detecting device for an automobile will be described in detail below with reference to FIGS.

FIG. 1 is an electric circuit diagram showing the construction of the oil level detecting device in this embodiment. This oil level detection device has a series circuit configuration in which a reed switch 1, an NTC type thermistor 2 and a warning lamp 3 are electrically connected in series. 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 1 is a float 12 which will be described later.
When the switch is turned on, the device can be energized. The thermistor 2 has a low resistance value 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.

Now, the characteristics of the thermistor 2 will be described in detail. The graph of FIG. 3 shows the relationship between the terminal voltage and the energization current of the thermistor 2 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 2 itself generates heat to cause thermal runaway when the increase in the energizing current exceeds the current value I1, and the resistance value gradually decreases.

The graph of FIG. 4 shows the relationship of the resistance value with respect to the ambient temperature of the thermistor 2 experimentally confirmed under a certain constant current value ("0.1 mA", "100 mA"). As you can see from this graph,
When a current of “0.1 mA” is applied, the resistance value gradually decreases to around “350 ° C.” as the ambient temperature rises, showing a characteristic suitable for temperature measurement.
On the other hand, when a current of "100 mA" is applied,
The resistance value drastically decreases at an ambient temperature of about “60 ° C.”. This is because the thermistor 2 itself rapidly generates heat and causes thermal runaway when the rise in the ambient temperature reaches almost “60 ° C.”.

The graph of FIG. 5 shows that a certain voltage ("12
V ”,“ 15V ”), the relationship between the ambient temperature of the thermistor 2 and the delay time of the switching operation confirmed experimentally. 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.”,
Approximately "55" for the voltages of "12V" and "15V"
Delay times of "second" and "40 seconds" are obtained.

In this embodiment, the thermistor 2 having the above characteristics and the reed switch 1 constitute a sensor circuit 5 incorporated in an oil level sensor 4 described later.

On the other hand, the warning lamp 3 is arranged in the combination meter in the driver's seat. The warning lamp 3 is turned on when a current of a predetermined value or more is supplied through the reed switch 1 and the thermistor 2, whereby the driver is warned that the oil is insufficient.

FIG. 2 is a sectional view showing the structure of the oil level sensor 4. The oil level sensor 4 includes a terminal housing 6 made of a conductive metal, and a connector 7 made of an insulating material is attached to the upper side of the housing 6. A terminal 8 for external output is fixed to the connector 7. The terminal 8 is connected to a battery (not shown) via the warning lamp 3 described above. On the other hand, on the lower side of the terminal housing 6, a base end portion of a protective pipe 9 made of a conductive metal is assembled. A pipe-shaped protective cover 10 is attached to the tip of the protective pipe 9. The thermistor 2 is fixed inside the tip of the protection pipe 9 via an insulator 11. The reed switch 1 is fixed inside the protective cover 10. Further, a ring-shaped float 12 is attached to the outer periphery of the protective cover 10 so as to be vertically movable. Further, a large-diameter stopper 13 made of a conductive metal is fixed to the tip of the protective cover 10, and the stopper 12 prevents the float 12 from coming off. Inside the float 12, a magnet 14 for operating the reed switch 1 is incorporated. The terminal 8 and one terminal of the thermistor 2 are connected by a lead wire 15. The other terminal of the thermistor 2 and one terminal of the reed switch 1 are connected to each other. Further, the other terminal of the reed switch 1 is connected to the stopper 13 and is grounded.

The oil level sensor 4 thus constructed is attached to the engine block 16 by the terminal housing 6 thereof, and the protective pipe 9 and the protective cover 10 thereof are contained in the engine oil of the oil pan 17 serving as a liquid reservoir. It is soaked in. In this state, if the engine oil amount is sufficient, the float 12 located in the engine oil will be located above the protective cover 10 in an attempt to float. As a result, the reed switch 1 is turned off, and the state in which electricity cannot be supplied is entered. On the other hand, when the amount of engine oil decreases and the oil level OL falls below a predetermined reference level, the float 12 located in the engine oil falls below the protective cover 10 as the level drops. Will be located.
As a result, the reed switch 1 is turned on by the magnetic force of the magnet 14 and becomes in a state capable of conducting electricity.

Next, the operation of the oil level detecting device constructed as described above will be described. The graph of FIG. 6 shows that when the engine oil amount is sufficient and the oil level OL is sufficiently high, the reed switch 1 is turned on / off with respect to the ambient temperature.
The relationship between off, the resistance value of the thermistor 2, and turning on / off of the warning lamp 3 is shown.

In this state, since the float 12 located in the engine oil is always located above the protective cover 10, the reed switch 1 is always off and in a non-energizable state. Therefore, no current flows from the battery to the thermistor 2 and the warning lamp 3. Then, in the thermistor 2, its resistance value shows only a slight change as the ambient temperature rises, and energization is not permitted. As a result, the warning lamp 3 remains off.

On the other hand, the graph of FIG. 7 shows that the oil level OL
Is lower than the reference level, that is, when the oil is insufficient, the reed switch 1 turns
The relationship between off, the resistance value of the thermistor 2, and turning on / off of the warning lamp 3 is shown.

In this state, since the float 12 located in the engine oil is located below the protective cover 10 as the oil level OL decreases, the reed switch 1 is turned on by the magnetic force of the magnet 14 and the energization is possible. Becomes Therefore, at the same time when the reed switch 1 is turned on, the battery voltage is applied to the thermistor 2. Then, in the voltage applied state, the thermistor 2
The resistance value of No. 2 sharply drops when the ambient temperature reaches almost "60 ° C". In addition, energization of the thermistor 2 is allowed due to the rapid decrease in the resistance value, and the oil level OL
The electric current as an electric signal for instructing the decrease of the electric current flows into the warning lamp 3 and the lamp 3 is turned on. Then, the driver is warned that the oil is insufficient.

Therefore, in this embodiment, when the atmospheric temperature is lower than "60 ° C." and therefore the oil viscosity is high, the thermistor 2 is allowed to be energized and the warning lamp 3 is not turned on. Therefore, in this embodiment, it is possible to prevent the lack of oil from being erroneously detected due to the decrease in the oil level OL when the oil level in the engine is drastically increased during cold weather. It is possible to prevent the warning from being given.

Further, in this embodiment, a delay time corresponding to the ambient temperature as shown in FIG. 5 is required before the energization of the thermistor 2 is allowed. Therefore, the lighting of the warning lamp 3 is substantially delayed for the delay time from when the reed switch 1 is turned on and the voltage is applied to the thermistor 2 until the energization of the thermistor 2 is allowed.

Therefore, in this embodiment, even if the engine oil amount is sufficient, even if the reed switch 1 is erroneously turned on due to the fluctuation / behavior of the oil level OL, from the time when the reed switch 1 is turned on. A delay of a delay time is given until the warning lamp 3 starts to light. As a result, it is possible to avoid erroneous detection of oil shortage due to fluctuations and behavior of the oil level OL. Moreover, in this embodiment, no special delay circuit is provided to set the delay time as described above. In other words, in this embodiment, a special delay circuit can be omitted, erroneous detection due to fluctuations and behavior of the oil level OL can be prevented, and highly reliable operation can be realized. is there.

Therefore, in this embodiment, the circuit configuration of the entire apparatus can be simplified by the amount that no special delay circuit is provided, and the cost increase of the apparatus can be suppressed.

Further, in this embodiment, the operation of the electric circuit as described above determines the oil shortage, and the warning lamp 3 is turned on / off according to the determination result. Therefore, in this embodiment, unlike the prior art, it is not necessary to provide a special ECU circuit for oil shortage determination. Further, the circuit configuration can be further simplified by omitting the ECU circuit, which can contribute to cost reduction of the device. Further, since the ECU circuit can be omitted, the mountability of the device on the vehicle can be improved accordingly.

(Second Embodiment) Next, a second embodiment in which the liquid level detecting device of the first and second inventions is embodied in an oil level detecting device for an automobile will be described in detail with reference to FIGS. 8 to 15. Explained.

FIG. 8 is an electric circuit diagram showing the structure of the oil level detecting device in this embodiment. The electrical configuration of this embodiment is basically the same as that of the first embodiment. That is, the reed switch 21, the thermistor 22, and the warning lamp 23 are electrically connected in series. 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 turned on by the movement of 5. Further, the thermistor 22 has a resistance value that becomes low after a predetermined time corresponding to the ambient temperature has passed after the voltage is applied, so that energization is allowed, and its characteristics are basically the same as those of the first embodiment. Are the same.

The lead switching 21 and the thermistor 22 constitute a sensor circuit 24 incorporated in an oil level sensor 25 described later. The warning lamp 23 is arranged in the driver's seat as in the first embodiment.

FIG. 9 is a sectional view showing the structure of the oil level sensor 25. The oil level sensor 25 includes a terminal housing 26 made of a conductive metal, and an upper side of the housing 26 has a connector 2 made of an insulating material.
7 is assembled. 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 its tip end side is an arm 29 extending horizontally. A cover 30 made of an insulating material is attached to the upper surface of the arm 29. Two terminals 31, 32 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. In addition, a plurality of holes 33a for venting air are formed at the base of the protection pipe 33.
Inside the protection pipe 33, the thermistor 2 described above is provided.
2 is fixed to the cover 30 and arranged. In addition, a pair of lead wires 22a, 22 extending from the thermistor 22.
b is connected to each of 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. At the lower end of the protection pipe 34, a stopper 36 made of a conductive metal having a larger diameter than the pipe 34 is provided.
Is stuck. Float 3 by this stopper 36
It has been equipped with 5 locks. Inside the float 35, a magnet 37 for operating the reed switch 21 is incorporated. Also, one lead wire 21a of the reed switch 21 penetrates the cover 30 and is connected to the terminal 32, and the other lead wire 21b is a 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 state, when the engine oil amount is sufficient, the float 35 located in the engine oil
Will hit the arm 29 and will be positioned above the protection pipe 34. As a result, the reed switch 21 is turned off so that it cannot be energized. On the other hand, when the amount of engine oil decreases and the oil level OL falls below a predetermined reference level, the float 35 located in the engine oil is located below the protection pipe 34 as the level drops. Will be done.
As a result, the reed switch 21 is turned on by the magnetic force of the magnet 37 and is in a state in which it can be energized.

In this embodiment, the positional relationship between the reed switch 21 and the thermistor 22 is set as follows. That is, as shown in FIG. 10, when the position at which the reed switch 21 is turned on by the float 35 is set to the reference level BL, the thermistor 22 is set to the reference level BL.
Is arranged in the vicinity of. Specifically, the thermistor 22
Is arranged above the reference level BL, and the relative height H between the reference level BL and the thermistor 22 is set to "5 mm" in this embodiment. This relative height H is
This is experimentally confirmed by the relationship between the average delay time obtained from the characteristics of the thermistor 22 and the average current flowing through the thermistor 22.

That is, the graph in FIG. 11 shows the relationship between the relative height H between the reference level BL and the lower end of the thermistor 22, the average current flowing through the thermistor 22, and the average delay time by the thermistor 22. In this graph,
Curves A and a indicated by solid lines show the vibration wave height of the oil level as "1.
The experimental result under the condition of "mm or less" is shown. Curves B and b indicated by a chain double-dashed line show the vibration wave height of the oil level as "3
mm ”and the vibration frequency thereof is“ 0.3 Hz ”. Also, the curves C and c shown by broken lines
Shows the experimental result under the condition that the vibration wave height of the oil surface is "3 mm" and the vibration frequency is "0.1 Hz". Further, in this graph, a region above the reference current value Ib indicates a “lighting region” in which the forning lamp 23 can be lit, and a region above the reference time Tb satisfies a practical delay time. "Practical area" is shown. Further, the position where the relative direction H is “0” is the reference level BL, the lower side of the reference level BL is “in liquid”, and the upper side is “in air”.

As is clear from this graph, all the curves A, B, C, a, b, c are the warning lamp 2
In "in the air" where 3 is to be lit, the average current value can satisfy the "lighting region" and the average delay time can satisfy the "practical region" at the relative height H of "5 mm". I understand. Therefore, in this embodiment, the relative height H is set to "5 mm".

Further, in this embodiment, the characteristics of the reed switch 21 are set as follows in order to prevent the reed switch 21 from being repeatedly turned on and off due to the fluctuation of the oil level. . That is, the reed switch 2
The strength of the magnetic field received from the magnet 37 when 1 is switched from the off state to the on state is set as a moving value Pi, and conversely, the strength of the magnetic field when the 1 is switched 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 moving value Pi is "0.2 to 0.6".
Is set in the range. Also, due to the difference in the moving range and moving direction of the magnet 37 with respect to the reed switch 21, the on / off switching of the reed switch 21 is performed with some hysteresis. In this example,
The hysteresis is defined as a “hold area”, and the “hold area” is set in the range of “0.5 to 3.5 mm”. That is, the ratio of the open value Do and the emotional value Pi (Do
The relationship of the "hold area" with respect to / Pi) is set so as to fall within the range indicated by the diagonal lines in the graph of FIG.

More specifically, FIGS. 13 (a) and 13 (b)
In, the reed switch 21 is turned on / off under the influence of the magnetic field of the magnet 37 that 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. Also, 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, so that the contact 21c becomes difficult to open. Therefore, as shown in FIG.
In No. 1, even if the magnet 37 moves to some extent, the ON state is maintained within the range affected by the magnetic field. Moreover, FIG.
As shown in FIG. 4, the moving range of the magnet 37 in which the reed switch 21 is held in the ON state 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 in the moving range. It becomes 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 steel of the contact 21c of the reed switch 21. In addition, the ratio of the open value Do and the emotional value Pi (Do /
The “hold area” is determined by Pi), the magnetized state of the magnet 37, and the like. 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.

Here, the lower limit value of the "hold area" in this embodiment, that is, "0.5 mm" is set on the basis of whether the reed switch 21 is repeatedly turned on and off, and the warning lamp 23 is blinking. Has been done. That is,
The graph of FIG. 15 shows the experimental results regarding the relationship between the size of the “hold area” and the number of times the warning lamp 23 blinks (times / second). In this experiment, the oil level O at which the warning lamp 23 is about to start lighting
L, that is, near the reference level BL described above. As is clear from this graph, the blinking of the warning lamp 23 indicates that the size of the "hold area" is "0.5".
It disappears in the vicinity of "mm". From this, the lower limit value of the "hold area" is set to "0.5 mm". On the other hand, the upper limit value of the "hold area" in the present embodiment, that is, "3.5 mm", the amplitude of the oil level in the oil pan 40 is usually "0.1-0.4 mm".
The vibration frequency is set to about "0.5 to 10 Hz", and the mass and shape of the float 35 are taken into consideration.

Next, the operation of the oil level detecting device constructed as described above will be described. Now, when the engine oil amount is sufficient and the oil level OL is sufficiently high, the reed switch 21 is always off because the float 35 located in the engine oil is located above the protection pipe 34. Therefore, no current flows from the battery to the thermistor 22 and the warning lamp 23. The resistance value of the thermistor 22 shows only a slight change as the ambient temperature rises.
Energization is never allowed. As a result, the warning lamp 23 remains off.

On the other hand, when the oil level OL is lower than the reference level, the float 35 located in the engine oil will be located below the protection pipe 34 as the oil level OL decreases. Therefore, the reed switch 21 is turned on by the magnetic force of the magnet 37. Therefore,
At the same time when the reed switch 21 is turned on, a voltage is applied to the thermistor 2 from the battery. Then, the resistance value of the thermistor 22 sharply decreases after a predetermined time corresponding to the ambient temperature has elapsed. Moreover, the thermistor 22 is thereby allowed to be energized, and a current as an electric signal for instructing the reduction of the oil level OL is supplied to the warning lamp 23.
Then, the lamp 23 is turned on and the driver is warned that the oil is insufficient.

Therefore, in this embodiment, when the ambient temperature is low and the oil viscosity is high, the thermistor 22 is allowed to be energized and the warning lamp 23 is not turned on. Therefore, in this embodiment, it is possible to prevent the oil shortage from being erroneously detected from the reduction of the oil level OL and to be erroneously warned when the oil level in the engine is drastically increased during cold weather. be able to.

Further, in this embodiment, the reed switch 2
A delay time corresponding to the ambient temperature is required from the time 1 is turned on until the energization of the thermistor 22 is allowed. Therefore, after the reed switch 21 is turned on and before the warning lamp 23 is turned on, a substantial delay is given by the delay time. Therefore, even if the engine oil amount is sufficient, fluctuations in the oil level OL
Even if the reed switch 21 is accidentally turned on due to the behavior, the warning lamp 23
Does not start lighting immediately, and a delay of a delay time occurs before lighting. As a result, it is possible to avoid erroneous detection of oil shortage due to fluctuations and behavior of the oil level OL. Moreover, also in this embodiment, no special delay circuit is provided to set the delay time as described above, so that the special delay circuit is omitted and the fluctuation / behavior of the oil level OL is caused. False detection can be prevented and a highly reliable operation can be realized. Therefore, in this embodiment, the circuit configuration of the entire device can be simplified by the amount that no special delay circuit is provided, and the cost increase of the device can be suppressed.

Further, in this embodiment, the electric circuit as described above is used to determine the lack of oil, and the warning lamp 23 is turned on and off. Therefore, also in this embodiment, it is not necessary to provide a special ECU circuit for determining the oil shortage, and the circuit configuration can be further simplified by omitting the ECU circuit, which contributes to the cost reduction of the device. be able to. Further, since the ECU circuit can be omitted, the mountability of the device on the vehicle can be improved accordingly.

Moreover, in this embodiment, the thermistor 22
By setting the relative height H between the reed switch 21 and the reed switch 21 to “5 mm”, the thermistor 22 is disposed near the reference level BL. Therefore, even if the oil level OL frequently changes in the vicinity of the reference level BL due to vibration of the automobile or the like, the thermistor 22 is always immersed in the engine oil.

Therefore, even if the reed switch 21 is frequently turned on and off due to the frequent fluctuations in the oil level OL, and the voltage is applied to the thermistor 22 each time, the thermistor 22 constantly heats the engine oil. Will be robbed. Therefore, the thermistor 22 does not accumulate heat due to frequent voltage application, and the delay time that should be secured by the thermistor 22 does not change. In addition, the warning lamp 23 does not blink instably due to this. As a result, a change in the oil level OL can be detected stably, and a stable operation of the warning lamp 23 can be ensured.

In addition, in this embodiment, regarding the characteristics of the reed switch 21, specific settings as shown in FIG. 12 are made. Therefore, even if the oil level fluctuates with a normal amplitude in the vicinity of the reference level BL, the reed switch 21 once turned on does not chatter and frequently turn on and off. As a result, the warning lamp 23 does not blink in an unstable manner, a change in the oil level OL can be detected stably, and a stable operation of the warning lamp 23 can be ensured. The setting related to the characteristic of the reed switch 21 is combined with the above-described setting related to the relative height H between the thermistor 22 and the reed switch 21 to provide a more advantageous synergistic effect in ensuring stable operation of the warning lamp 23. Will bring.

The present invention is not limited to the above-described embodiments, but may be implemented as follows with a part of the structure appropriately changed without departing from the spirit of the invention. (1) In each of the above-described embodiments, the liquid level detecting device is embodied as the oil level detecting device applied to the oil pans 17 and 40 of the automobile. You can also In that case,
You may change the shape of an apparatus suitably according to a tank.

(2) In each of the above embodiments, the sensor circuit 5,
Although the oil level sensors 4 and 25 having the built-in 24 and the warning lamps 3 and 23 are separately configured, the oil level sensor having the built-in sensor circuit and the warning lamp may be integrally provided.

(3) In the second embodiment, the reference level B
Although the relative height H between L and the thermistor 22 is set to "5 mm" based on the experiment, the relative height may be appropriately changed depending on the characteristics of the thermistor and the temperature conditions used.

(4) In the second embodiment, the characteristic of the reed switch 21 is set as shown in FIG. 12, but the setting is made with respect to the characteristic of the reed switch 1 in the oil level sensor 4 of the first embodiment. You can do the same.

[0057]

As described above in detail, according to the first aspect of the present invention, the switch that is turned on when the liquid level becomes lower than the reference level in the liquid reservoir and the ambient temperature after the voltage is applied. Is electrically connected in series with a thermistor whose resistance value decreases after a predetermined time corresponding to
Therefore, the output of the electric signal for instructing the lowering of the liquid level is delayed only for a predetermined time from when the switch is turned on until the energization of the thermistor is allowed. As a result, it is possible to omit the special delay circuit and prevent the erroneous detection due to the fluctuation / behavior of the liquid level.

According to the second aspect of the invention, in the liquid reservoir, a voltage is applied at the same time when the liquid level becomes equal to or lower than the reference level, and a predetermined time corresponding to the ambient temperature in the liquid reservoir after the voltage is applied. A thermistor whose resistance value becomes low after the passage of is placed near the reference level in the liquid reservoir. Therefore, the output of the electric signal for instructing the lowering of the liquid level is delayed for a predetermined time until the energization of the thermistor is permitted. In addition, even if the liquid level frequently changes in the vicinity of the reference level, the thermistor is always immersed in the liquid to remove heat, and the delay action of the thermistor does not become unstable. As a result, even if the liquid level changes frequently, the excellent effect that stable detection can be performed is exhibited.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing a configuration of an oil level detection device according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a structure of an oil level sensor and the like in the first embodiment.

FIG. 3 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.

FIG. 4 is a graph showing the relationship between the resistance value and the ambient temperature of the thermistor experimentally confirmed under a constant current value in the first embodiment.

FIG. 5 is a graph showing the relationship between the ambient temperature of the thermistor and the delay time of the switching operation experimentally confirmed under a constant voltage in the first embodiment.

FIG. 6 is a graph showing a relationship between ON / OFF of a reed switch, a resistance value of a thermistor, and turning on / off of a warning lamp with respect to an ambient temperature when the oil level is high in the first embodiment.

FIG. 7 is a graph showing a relationship between ON / OFF of a reed switch, a resistance value of a thermistor, and turning on / off of a warning lamp with respect to an ambient temperature when the oil level is low in the first example.

FIG. 8 is an electric circuit diagram showing a configuration of an oil level detection device according to a second embodiment of the present invention.

FIG. 9 is a sectional view showing the structure of an oil level sensor and the like in a second embodiment.

FIG. 10 is a diagram showing a positional relationship between a reference level of a reed switch and a thermistor in the second embodiment.

FIG. 11 is a graph showing the relationship between the relative height between the reference level and the thermistor, the average current flowing through the thermistor, and the average delay time due to the thermistor in the second embodiment.

FIG. 12 is an opening value Do and a moving value P in the second embodiment.
It is a graph which shows the relation of the "hold area" with respect to the ratio (Do / Pi) with i.

FIG. 13 is an explanatory diagram for explaining the operation of the reed switch and the positional relationship of the magnets in the second embodiment.

FIG. 14 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 second embodiment.

FIG. 15 is a graph showing the relationship between the number of blinks of the warning lamp and the “hold area” in the second example.

[Explanation of symbols]

1 ... Reed switch, 2, 22 ... Thermistor, 17, 4
0 ... Oil pan as liquid reservoir, OL ... Oil level as liquid level, BL ... Reference level.

Claims (2)

[Claims] 1. A switch that is turned on when the liquid level in a liquid reservoir falls below a predetermined reference level, and a predetermined time that is arranged in the liquid reservoir and that corresponds to the ambient temperature after a voltage is applied. A liquid level detection device, comprising: a thermistor whose resistance value decreases after a lapse of time, wherein the switch and the thermistor are electrically connected in series. 2. A resistance value after a voltage is applied at the same time as the liquid level becomes equal to or lower than a predetermined reference level in the liquid reservoir, and a predetermined time corresponding to the ambient temperature in the liquid reservoir elapses after the voltage is applied. A liquid level detecting device comprising: a thermistor that lowers the temperature, and the thermistor is disposed in the liquid reservoir in the vicinity of the reference level.