JPH06317448A - Oil level sensor - Google Patents

Abstract

PURPOSE:To allow accurate detection of oil level over the entire operating temperature range even for a wide operating temperature range. CONSTITUTION:A thermister 20 is secured to the sensor fixing part 16 of a sensor stay 12 provided for an oil pan 10. The thermister 20 is located to be immersed into the oil 18 or not depending on the increase/decrease of oil 18 in the oil pan 10 so that the thermister 20 is self-heated to cause variation of resistance when it is immersed into the oil 18 and not. Another thermister 22 is fixed to a sensor fixing part 14. The thermister 22 is located to be immersed into the oil 18 at all times so that the thermister 2 is not self-heated but feeds a conduction current and serves as a monitor for oil temperature. The thermisters 20, 22 are connected with comparing circuits, respectively, wherein the thermister 20 is connected, at one terminal thereof, with the comparison voltage input terminal of the comparator. The thermister 22 is connected, at one terminal thereof, with the voltage reference input terminal of the comparator.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oil level sensor, and more particularly to an oil level sensor for detecting whether or not a predetermined amount of oil is present in an oil pan of a vehicle such as an automobile.

[0002]

2. Description of the Related Art Conventionally, as for an oil level sensor for detecting whether or not a predetermined amount of oil is present in an oil pan of a vehicle such as an automobile, a thermistor serving as a temperature sensing element is caused to self-heat so that the oil It is known that the presence or absence of oil is determined by detecting a resistance difference caused by a difference in heat radiation efficiency between air and air.

As shown in FIG. 4, in the comparison circuit 70 of this oil level sensor, the reference voltage Vt of the comparator 72 is R1 / (the resistance value R1 of the resistor 74 and the resistance value R2 of the resistor 76 with respect to the power source voltage V). R1 + R2) .V. The voltage Vp of the thermistor 78 is larger than the reference voltage to detect whether or not a predetermined amount of oil is present in the oil pan. That is, as shown in the area A of FIG. 5, the voltage Vpa when the thermistor 78 is in the air becomes higher than the reference voltage Vt, and the voltage Vpo when the thermistor 78 is in the oil becomes lower than the reference voltage Vt. Therefore, it is detected whether or not there is a predetermined amount of oil in the oil pan.

[0004]

However, in the case of detecting a liquid such as engine oil, which has a drastic temperature change, the resistance of the thermistor which self-heats greatly changes depending on the ambient temperature. . Therefore, when the measured temperature range is wide as shown in the area B of FIG. 5,
In the high temperature region (region C in FIG. 5), the voltage Vpo when the thermistor 78 is in oil also exceeds the reference voltage Vt, so it is possible to detect whether or not a predetermined amount of oil is present in the oil pan. Disappear.

On the other hand, the reference voltage Vt is set to Vs higher than Vt.
When the temperature is set to, when the air temperature is X ° C or lower, the voltage Vpa when the thermistor 78 is in the air becomes the reference voltage Vs or lower. It becomes impossible to detect whether or not there is a predetermined amount of oil.

For this reason, it is difficult to accurately detect the oil level in the entire operating temperature range.

In view of the above facts, an object of the present invention is to provide an oil level sensor capable of accurately detecting the oil level in the entire operating temperature range even when the operating temperature range is wide. .

[0008]

SUMMARY OF THE INVENTION An oil level sensor according to the present invention includes a first temperature sensitive element provided at a position where the oil level in an oil pan changes depending on the increase / decrease of the oil in the oil pan, and the oil level sensor always operates. A second temperature sensitive element provided at a position that is either in the oil or in the air in the pan, and the first temperature sensitive element based on the temperature data from the second temperature sensitive element. And a comparison circuit for judging the presence or absence of oil in the oil pan from the temperature data of the element.

[0009]

In the oil level sensor according to the present invention, the temperature of the oil in the oil pan is adjusted by the second temperature sensing element provided at a position that is always either in the oil in the oil pan or in the air. Alternatively, by monitoring the air temperature in the oil pan, the reference voltage, which has been a constant value in the past, is changed according to the monitored temperature.
That is, based on the temperature data from the second temperature sensitive element,
Since the presence or absence of oil in the oil pan is determined from the temperature data of the first temperature sensing element, the reference value of the comparison circuit changes when the temperature in the oil pan changes significantly. Therefore, the reference value is always located between the temperature data when the first temperature sensing element is in oil and the temperature data when the first temperature sensing element is in air. Therefore, even when the operating temperature range is wide, it is possible to always accurately detect the oil level in the entire operating temperature range. An energizing current that does not generate heat is applied to the second temperature sensitive element.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the oil level sensor of the present invention will be described with reference to FIGS.

As shown in FIG. 1, a sensor stay 12 is provided in an oil pan 10 provided in the lower portion of the engine, and an upper end portion 12A of the sensor stay 12 is provided.
Is fixed to the inner wall portion 10A of the oil pan 10. The sensor stay 12 extends downward, and the lower end portion 12B of the sensor stay 12 extends substantially parallel to the bottom portion 10B of the oil pan 10.

At the lower end portion 12B of the sensor stay 12, 2
The sensor mounting portions 14 and 16 of the book are formed in parallel downward, and the sensor mounting portion 14 is longer than the sensor mounting portion 16.

A thermistor 20 as a first temperature sensitive element is fixed to the lower end 16A of the sensor mounting portion 16. That is, this thermistor 20 is below the liquid level 18A of the oil 18 when the oil 18 in the oil pan 10 increases as shown by the phantom line in FIG. 1, and as shown by the solid line in FIG. When the oil 18 in the pan 10 is reduced, it is on the liquid surface 18A of the oil 18. In addition, the thermistor 20 is supplied with an energizing current that self-heats to cause resistance change inside and outside the oil 18 due to self-heating.

A thermistor 22 as a second temperature sensitive element is fixed to the lower end portion 14A of the sensor mounting portion 14. That is, the thermistor 22 is provided at a position in the oil 18 even when the oil 18 in the oil pan 10 is reduced, and it is used as a monitor of the oil temperature by passing an energizing current that does not generate heat by itself.

As shown in FIG. 2, the thermistor 20 and the thermistor 22 are connected to a comparison circuit 26, respectively. One terminal 20A of the thermistor 20 is grounded, and the other terminal 20B of the thermistor 20 is connected to a power supply 32 via a resistor 30. Also, the thermistor 20
20B is connected to the comparison voltage input terminal 34A of the comparator 34.

On the other hand, one terminal 22A of the thermistor 22
Is grounded, and the other terminal 22B of the thermistor 22
Is connected to the power supply 32 via the resistor 36. Also,
The terminal 22B of the thermistor 22 is connected to the reference voltage input terminal 34B of the comparator 34.

The output terminal 34C of the comparator 34
Is connected to an oil presence / absence display device (not shown), and the presence / absence of oil is displayed on the oil presence / absence display device based on the output signal from the output terminal 34C of the comparator 34.

Next, the operation of this embodiment will be described. In the oil level sensor of this embodiment, the reference voltage input to the comparator 34 is obtained by monitoring the temperature of the oil 18 in the oil pan 10 by the thermistor 22 provided at a position that is always in the oil 18 in the oil pan 10. The reference voltage Vt at the terminal 34B is as shown in FIG.
It rises as the temperature inside the oil pan 10 rises. That is, the reference temperature, which has been a constant value in the past, changes depending on the temperature of the oil 18 monitored by the thermistor 22.

As described above, in the oil level sensor of this embodiment, the reference voltage Vt which changes with the temperature of the oil 18 is used.
Since the presence or absence of the oil 18 in the oil pan 10 is determined from the temperature data of the thermistor 20 with reference to the above, even when the temperature in the oil pan 10 greatly changes, as shown in FIG. The voltage Vpo when 18 is present and the voltage Vpa when the thermistor 20 is in air
And the reference voltage Vt is located between the two. Therefore, even when the operating temperature range is wide, it is possible to always accurately detect the oil level in the entire operating temperature range.

In the oil level sensor of this embodiment, the thermistor 22 is provided at a position in the oil pan 10 that is always in the oil and used as a monitor of the oil temperature. Instead, the thermistor 22 is used. Alternatively, it may be provided at a position in the oil pan 10 that is always in the air and used as a monitor of the air temperature.

Further, in the oil level sensor of this embodiment, the thermistor is used as the temperature sensing element, but the resistance value increases as the temperature rises instead of the thermistor.
A so-called posistor may be used. Furthermore, if a processing circuit is added, a thermocouple can be used.

[0022]

The oil level sensor according to the present invention comprises a first temperature sensitive element provided at a position where the oil level in the oil pan changes depending on the amount of the oil in the oil pan, and the oil always in the oil pan. A second temperature sensitive element provided at a position that is either inside or in the air, and oil based on the temperature data of the first temperature sensitive element based on the temperature data of the second temperature sensitive element. Since it is configured to have a comparison circuit that determines the presence or absence of oil in the pan, even if the operating temperature range is wide, it is possible to accurately detect the oil level in the entire operating temperature range. Have an effect.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view showing an oil pan to which an oil level sensor according to an embodiment of the present invention is applied.

FIG. 2 is a circuit diagram showing an oil level sensor according to an embodiment of the present invention.

FIG. 3 is a graph showing the relationship between the detected voltage and the temperature of the oil level sensor according to the embodiment of the present invention.

FIG. 4 is a circuit diagram showing an oil level sensor according to a conventional example.

FIG. 5 is a graph showing a relationship between a detected voltage of an oil level sensor and a temperature according to a conventional example.

[Explanation of symbols]

 10 oil pan 12 sensor stay 14 sensor mounting portion 16 sensor mounting portion 18 oil 20 thermistor (first temperature sensitive element) 22 thermistor (second temperature sensitive element) 26 comparison circuit 34 comparator

Claims (1)

[Claims] 1. A first temperature-sensing element provided at a position where the oil in the oil pan changes into and out of the air depending on the increase / decrease in the oil in the oil pan, and either in the oil or in the air always in the oil pan. The presence or absence of oil in the oil pan is determined from the temperature data of the second temperature sensing element provided at one position and the temperature data of the first temperature sensing element as a reference. An oil level sensor, comprising: a comparison circuit for judging.