JP2006017588A - Level detection device and level detection method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a level detection device and its method capable of detecting a liquid level in a wide range continuously, based on the principle of level detection by the difference between the specific heat capacities of a gas and a liquid. <P>SOLUTION: The device is provided with a resistor 1a having a length in the direction of liquid filling exceeding a desired liquid level detection range, an ambient temperature detection means 1b for detecting an ambient temperature around the resistor, a temperature difference setting means S211-S214 which uses, as a target temperature T for heating the resistor, a temperature to be obtained by adding a predetermined temperature difference ΔT to the ambient temperature (reference temperature T0) detected by the ambient temperature detection means, a resistor temperature detection means S221-223 for detecting the temperature of the resistor, a power control means S221-S225 which controls power to be supplied to the resistor to heat the resistor to the target temperature T, and controls the power so as to maintain the resistor temperature at the target temperature, when the temperature reaches the target temperature, a power calculation means S231 for calculating the magnitude of the power being supplied to the resistor from the power control means, and a liquid level determination means S232 for detecting the liquid level on the basis of the magnitude of the power. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a liquid level detection device and a liquid level detection method, and is suitable for application to, for example, a liquid level detection device and a liquid level detection method for detecting the oil level of hydraulic fluid of an internal combustion engine for a vehicle or the like. .

  Some liquid level detection devices detect the remaining amount of engine oil or the like in an oil pan as a liquid filled in an internal combustion engine such as a vehicle (see Patent Documents 1, 2, and 3). This type of liquid level detection device includes a so-called temperature-dependent resistor whose resistance value changes with temperature, and the heat of the resistor is easily taken away by the liquid due to the difference in specific heat between the gas and the liquid. The liquid level is detected by utilizing the fact that it is difficult to be taken away by the gas.

  In the technique disclosed in Patent Document 1, after the resistor is heated from the reference value corresponding to the ambient temperature to the upper threshold value that is a predetermined temperature difference, the heat dissipation time required for the temperature to drop to the reference value is reduced. For example, the longer the heat dissipation time, the higher the rate at which the resistor is exposed in the gas, and the liquid level is detected.

In the techniques disclosed in Patent Documents 2 and 3, a thermistor or the like is used as a resistor, and this resistor is provided at a position where the resistor changes from, for example, gas to liquid.
German patent DE 374 2783 specification JP-A-6-317448 JP-A-10-176944

  In the prior art of Patent Document 1, since the liquid level is detected by using the heat dissipation time or the change in resistance value during the heat dissipation period of the resistor, the heating period for heating the resistor cannot be detected. There is a problem that the level can only be detected intermittently.

  In the prior arts of Patent Documents 2 and 3, the liquid level can be detected continuously. However, since only one arbitrary point where the resistor is installed can be detected, there is a problem that the detection range of the liquid level is narrow.

  The present invention has been made in consideration of such circumstances, and its purpose is to detect the liquid level based on the difference in specific heat between gas and liquid, and continuously detect the liquid level in a wide range. An object of the present invention is to provide a liquid level detection device and a liquid level detection method.

  According to claim 1 of the present invention, a temperature-dependent resistor whose resistance value changes according to temperature is provided, and the resistor is placed in a portion corresponding to the liquid level to be detected in the container in which the liquid is stored. In the liquid level detection device that detects the liquid level using the difference between the specific heat of gas and liquid, the resistor has a length in the liquid filling direction that exceeds the range of the liquid level to be detected. The ambient temperature detecting means arranged side by side on the resistor and detecting the ambient temperature around the resistor, and the temperature obtained by adding or subtracting a predetermined temperature difference to the ambient temperature detected by the ambient temperature detecting means A temperature difference setting means for setting the target temperature for heating or cooling, a resistor temperature detection means for detecting the temperature of the resistor, and a resistor for heating or cooling the resistor to the target temperature set by the temperature difference setting means Control the power supplied to the body, When the temperature of the resistor reaches the target temperature, a power control unit that controls the power to maintain the target temperature, a power calculation unit that calculates the amount of power supplied from the power control unit to the resistor, and power A liquid level determining means for detecting the liquid level based on the magnitude of the electric power calculated by the calculating means is provided.

  According to this, the resistor is formed so that the length in the liquid level filling direction exceeds the range of the liquid level to be detected. Furthermore, ambient temperature detection means for detecting the ambient temperature around the resistor is arranged side by side on the resistor. A temperature difference setting means for setting a target temperature at which a difference from the ambient temperature becomes a predetermined temperature difference, and for example, when the target temperature set by the temperature setting means is higher than the ambient temperature, the resistor is heated to the target temperature. Therefore, power control means is provided for controlling the power supplied to the resistor and controlling the power so as to maintain the target temperature when the temperature of the resistor reaches the target temperature. As a result, the resistor can efficiently transfer heat to and from the gas and the liquid, and the interface between the gas and the liquid is utilized by taking advantage of the fact that the liquid is easily deprived of the heat of the resistor and not easily deprived of the gas. The liquid level can be detected over the entire range of the liquid level to be detected. Furthermore, since the temperature of the resistor is maintained at the target temperature by the power control means, it is maintained at the target temperature as compared with the conventional case in which the liquid level is detected by a change in the cooling time or resistance value during, for example, transient cooling. During this period, the liquid level can be repeatedly measured. Therefore, it is possible to continuously detect the liquid level by heating or cooling the resistor to a target temperature at which the temperature difference from the ambient temperature becomes a predetermined temperature difference by the power control means.

  According to the second aspect of the present invention, the resistor and the ambient temperature means are arranged on a single substrate, and the substrate has a substantially slit shape penetrating the front surface and the back surface between the resistor and the ambient temperature detection means. The opening part is provided.

  According to this, when the resistor and the ambient temperature detecting means are arranged on a single substrate, a substantially slit-like opening that penetrates the front and back surfaces of the substrate is provided between the resistor and the ambient temperature detecting means. Therefore, the heat can be blocked by the space of the substantially slit-shaped opening so that the heat generated by the resistor does not directly affect the ambient temperature detecting means. Therefore, even when the resistor is heated to the target temperature by the power control means and a temperature difference occurs with the ambient temperature, the ambient temperature detection means independently detects the ambient temperature around the resistor. be able to.

  According to a third aspect of the present invention, the ambient temperature detecting means includes a first thermistor disposed in the liquid.

  According to this, until reaching a predetermined number of repetitions of repeating the heating of the resistor, etc., where the difference between the temperature of the liquid constituting the ambient temperature and the temperature of the gas is relatively small, or the difference becomes a problem, for example, Continuous measurement of liquid level is possible.

  According to a fourth aspect of the present invention, the ambient temperature detecting means includes a second thermistor disposed in the gas.

  According to this, the first thermistor and the second thermistor are provided, and the temperature of the liquid and the temperature of the gas are detected by these thermistors. Therefore, for example, correction by weighting or the like is performed based on the temperature of the liquid and the temperature of the gas. Thus, it is possible to detect the ambient temperature without error.

  According to claim 5 of the present invention, the ambient temperature detecting means includes a second resistor different from the resistor, and the second resistor has the same temperature-dependent characteristics as the resistor.

  According to this, it is preferable that the ambient temperature detection means includes a second resistor different from the resistor, and the second resistor has the same temperature-dependent characteristics as the resistor. Thereby, for example, based on the difference between the individual resistors and the second resistor, it is easy to correct the resistance value related to the temperature detection between the two resistors.

  According to claim 6 of the present invention, the power control means corrects the ambient temperature detection means with a correction value based on a temperature difference between the temperature of the resistor and the ambient temperature before supplying power to the resistor. And a reference temperature compensating means for setting the temperature of the ambient temperature detecting means corrected by the correction value to a temperature before supplying power to the resistor.

  According to this, the power control means corrects the ambient temperature detection means with a correction value based on a temperature difference between the temperature of the resistor and the ambient temperature before supplying power to the resistor, and corrects with the correction value. And a reference temperature compensation means for setting the temperature of the ambient temperature detecting means to a temperature before supplying power to the resistor, so that the detection accuracy for detecting the temperature of the resistor for detecting the liquid level can be improved. I can plan. For example, when the resistor is maintained at the target temperature by the power control of the power control means, not only the temperature difference between the resistor temperature and the target temperature before heating the resistor but also the state in which the target temperature is maintained is being heated. The temperature difference between the temperature of the resistor and the temperature of the resistor before heating, that is, the ambient temperature can be set to a predetermined temperature difference by the reference temperature compensation means. As a result, it is possible to improve the detection accuracy for detecting the liquid level based on the power level by the liquid level determination means.

  According to claim 7 of the present invention, the power control means detects the resistance value of the resistor and the resistance value of the second resistor before supplying power to the resistor, and based on the difference between these resistor values. Correction means for correcting the resistance value of the second resistor by the correction value; and reference temperature compensation means for setting the resistance value of the second resistor corrected by the correction value to the resistance value before supplying power to the resistor; It is characterized by having.

  According to this, the power control means detects the resistance value of the resistor and the resistance value of the second resistor before supplying power to the resistor, and the second value is determined by a correction value based on the difference between these resistor values. Correction means for correcting the resistance value of the resistor, and reference temperature compensation means for using the resistance value of the second resistor corrected by the correction value as the resistance value before supplying power to the resistor. The detection accuracy for detecting the temperature of the resistor for detecting the liquid level can be improved.

According to the eighth aspect of the present invention, the temperature-dependent resistor whose resistance value changes according to the temperature is arranged in a portion corresponding to the liquid level to be detected in the container in which the liquid is stored, and the gas In the liquid level detection method that detects the liquid level using the difference between the specific heat of the liquid and the liquid,
Form the length of the resistor in the liquid filling direction so that it exceeds the range of the liquid level that you want to detect,
Ambient temperature detection means for detecting the ambient temperature around the resistor is arranged side by side on the resistor,
A temperature difference setting step in which a temperature obtained by adding or subtracting a predetermined temperature difference to the ambient temperature detected by the ambient temperature detection means is set as a target temperature for heating or cooling the resistor;
A power supply stage for supplying power to the resistor to heat or cool the resistor to a target temperature;
A power control stage that controls the power supplied to the resistor so that the target temperature is maintained when the temperature of the resistor reaches the target temperature;
A power calculation stage for calculating the magnitude of power when the temperature of the resistor is maintained at the target temperature;
A liquid level determination step for detecting the liquid level based on the magnitude of the electric power calculated in the power calculation step.

  According to this, the length of the resistor in the liquid filling direction is formed so as to exceed the range of the liquid level to be detected. Further, ambient temperature detecting means for detecting the ambient temperature around the resistor is arranged side by side on the resistor. A temperature difference setting stage in which a temperature obtained by adding or subtracting a predetermined temperature difference to the ambient temperature detected by the ambient temperature detection means is set as a target temperature for heating or cooling the resistor, and the resistor is heated or cooled to the target temperature. A power supply stage for supplying power to the resistor, a power control stage for controlling the power supplied to the resistor so that the target temperature is maintained when the temperature of the resistor reaches the target temperature, and the temperature of the resistor A power calculation stage for calculating the power level when the temperature is maintained at the target temperature, and a liquid level determination stage for detecting the liquid level based on the power level calculated in the power calculation stage. ing. As a result, the resistor can efficiently transfer heat to and from the gas and the liquid, and the interface between the gas and the liquid is utilized by taking advantage of the fact that the liquid is easily deprived of the heat of the resistor and not easily deprived of the gas. The liquid level can be detected over the entire range of the liquid level to be detected. In addition, power is supplied to the resistor to heat or cool the resistor to the target temperature in the power supply stage, and in the power control stage, the target temperature is maintained when the temperature of the resistor reaches the target temperature. Since the power supplied to the resistor is controlled, the power control stage is maintained at the target temperature, compared to the conventional method in which the liquid level is detected by, for example, the cooling time during transient cooling or the change in resistance value. If it exists, the liquid level can be repeatedly measured. Therefore, it is possible to detect the liquid level continuously by performing power control for maintaining the target temperature at which the temperature difference between the resistor and the ambient temperature becomes a predetermined temperature difference in the power control stage.

  According to claim 9 of the present invention, before the start of the power supply stage, the temperature of the resistor and the temperature of the ambient temperature detection means are detected, and the temperature of the ambient temperature detection means is corrected by a correction value based on the difference between these temperatures. A correction stage is provided.

  According to this, before the start of the power supply stage, there is provided a correction stage for detecting the temperature of the resistor and the temperature of the ambient temperature detection means, and correcting the temperature of the ambient temperature detection means by a correction value based on the difference between these temperatures. It is preferable. Thereby, the detection accuracy for detecting the temperature of the resistor for detecting the liquid level can be improved. For example, when power is supplied to the resistor by power supply means and the resistor is maintained at the target temperature by power control in the power control stage, not only the temperature difference between the resistor temperature and the target temperature before heating the resistor The temperature difference between the temperature of the resistor being heated, including the state in which the target temperature is maintained, and the temperature of the resistor before heating, that is, the ambient temperature, is resisted by the temperature of the ambient temperature detecting means corrected by executing the correction stage. By setting the resistance value before power supply to the body, it is possible to set a predetermined temperature difference. As a result, it is possible to improve the detection accuracy for detecting the liquid level based on the power level by the liquid level determination means.

  The ambient temperature detecting means may be any one provided with a thermistor disposed in the liquid or a second resistor having the same temperature dependency as the resistor and different from the resistor.

  According to claim 10 of the present invention, the power supply stage is repeated a plurality of times until the power control stage is reached, and the temperature of the ambient temperature detecting means is corrected based on the correction value immediately before each power supply stage. The target temperature is corrected based on the measured temperature. According to this, the power supply stage is repeated a plurality of times until the power control stage is reached, and immediately before each power supply stage, the temperature of the ambient temperature detecting means is corrected based on the correction value, and based on this corrected temperature. It is preferable to correct the target temperature. Thereby, the temperature difference between the target temperature for heating or cooling the resistor and the ambient temperature is always maintained at the same predetermined temperature difference. As a result, in the power control stage, power control can be performed with the magnitude of power corresponding to a predetermined temperature difference.

  Hereinafter, the liquid level detection device and the liquid level detection method of the present invention are applied to an oil level detection device that detects the level of engine oil filled in an internal combustion engine (hereinafter referred to as an engine) mounted on a vehicle or the like. Embodiments applied and embodied will be described with reference to the drawings.

  FIG. 1 is a configuration diagram showing the configuration of the liquid level detection device of the present embodiment. FIG. 2 is a flowchart showing a liquid level detection process performed by the control circuit in FIG. FIG. 3 is a graph showing the relationship between the resistance value and temperature of the resistor and the second resistor in FIG. FIG. 4 is a graph showing the relationship between the electric power used for the control process in step 232 in FIG. 2 and the liquid level. FIG. 5 is a time chart showing one embodiment of the liquid level detection process in FIG. 2 in time series.

  As shown in FIG. 1, the liquid level detection device is used to lubricate an engine for a vehicle such as an automobile, and detects the remaining amount of engine oil 4 as a liquid. The engine oil 4 is stored in a tank (hereinafter referred to as an oil pan) 5 disposed at the lower part of the engine.

  As shown in FIG. 1, the liquid level detection device includes a resistor (hereinafter referred to as a detection resistor) 1a and a second resistor (hereinafter referred to as a reference resistor) 1b different from the resistor 1a. And the control circuit 2. The detection resistor 1 a and the reference resistor 1 b are arranged in a cylindrical insertion member (hereinafter referred to as a case) 6. The case 6 is arranged in a substantially vertical direction (the filling direction of the engine oil 4 in FIG. 1) from the lower side to the upper side of the oil pan 5, and the gas such as the engine oil 4 in the oil pan 5 and air described later is the case 6. A passage hole 7 is provided to allow the inside to flow. The passage hole 7 alleviates unnecessary liquid level fluctuation around the periphery of the detection resistor 1a and the reference resistor 1b. In this case 6, a base 6 a is sealed at the opening of the substantially bottomed cylindrical case 6, and the case 6 is inserted from the outside to the inside of the oil pan 5 and is airtightly fixed to the oil pan 5. The control circuit 2 is disposed outside the oil pan 5 and connected so as to be electrically connected to the detection resistor 1a and the reference resistor 1b. The control circuit 2 is added to a circuit of other control means (hereinafter referred to as ECU) on the vehicle (not shown) as a separate body, even if the control circuit 2 is arranged to be attached to the lower portion of the base 6a. Also good. The ECU may control an engine, a vehicle control device such as a vehicle transmission device or a brake device, or an engine and a vehicle control device, or an engine having an oil pan 6 or the like. Any control device may be used.

  The detection resistor 1a and the reference resistor 1b constitute detection means (hereinafter referred to as an oil level sensor) for detecting the liquid level of the engine oil 4. When the control circuit 2 is integrated with the oil level sensor 1, the oil level sensor 1 and the control circuit 2 constitute an oil level sensor module. The size of the case 6 (specifically, the outer diameter in FIG. 1) is set to a relatively large outer diameter because heat is generated from the detection resistor 1a, but the liquid level fluctuates as the outer diameter increases. Therefore, the outer diameter is set to a predetermined size in consideration of influence factors such as the heat radiation amount of the detection resistor 1a and the fluidity of the engine oil targeted for the detection liquid level.

  The detection resistor 1a and the reference resistor 1b are so-called temperature-dependent resistors (hereinafter referred to as temperature resistors) whose resistance values change according to temperature. The detection resistor 1a and the reference resistor 1b are two identical temperature resistors as shown in FIG. As shown in FIG. 1, the detection resistor 1a and the reference resistor 1b are provided with a conductive wiring member (hereinafter referred to as a pattern member) as a resistance pattern on a substrate. As a material, a material having a relatively large resistance temperature coefficient such as nickel or tungsten is used. As shown in FIG. 1, these resistors 1a and 1b are disposed in the engine oil filling direction exceeding the range of the liquid level 3 level to be detected in the oil pan 5, that is, the case 6 (from the lower side to the upper side in FIG. 1). The length of the vertical direction). The range of the liquid level 3 to be detected refers to the lower part of the pattern member applied to the resistors 1a and 1b from the lowest end (the position where the liquid level is 0 in FIG. 1), for example, engine lubrication. This is a range that is the uppermost end of the liquid level 3 level (position L in FIG. 1) from the viewpoint of the function of the liquid 4 such as the liquid level 3 corresponding to the required amount of engine oil. The liquid level 3 is an interface between the engine oil 4 and a gas such as air facing the engine oil 4 filled in the oil pan 5. Thereby, these resistors 1a and 1b can efficiently transfer heat with engine oil and air. In addition, for example, immediately before power is supplied to the oil level sensor 1, the resistors 1a and 1b can follow the ambient temperature. In this case, the ambient temperature is a temperature detected by the resistors 1a and 1b determined from the transfer of heat of the engine oil 4 and air corresponding to the level 3 of the liquid level to be detected. The engine oil 4 temperature and the ambient temperature Is the average temperature at which equilibrium occurs. Note that a pattern member may be provided inside the substrate. In that case, it is preferable to select a substrate material that does not affect the transfer of heat between the engine oil 4 and air.

  The control circuit 2 includes a heating control unit (hereinafter referred to as a heating circuit) 2g, a detection unit (hereinafter referred to as a detection circuit) 2i, a control calculation unit (hereinafter referred to as a control calculation circuit unit) 2h, and a heating circuit 2g. It is configured to include a switching element (hereinafter referred to as switching SW) 2f that controls heating of the detection resistor 1a by a signal and load resistors 2a, 2b, 2c, and 2d.

  Both ends (hereinafter referred to as first ends) of the pattern member of the detection resistor 1a have a well-known configuration that can be electrically connected to the outside (not shown), and one ends of the first ends ( As shown in FIG. 1, the first end is connected to a power source (not shown) (part of voltage V0 in FIG. 1) via load resistors 2a and 2b connected in series. One end of load resistors 2d and 2e connected in series is connected to a middle point (referred to as a first middle point) connecting the load resistor 2a and the load resistor 2b, and the other end is electrically grounded. Grounded. The other end of the first both ends (hereinafter referred to as the first other end) is connected to the other end. As shown in FIG. 1, the second ends of the second end portions of the pattern member of the reference resistor 1b are connected to a power source via a load resistor 2c. The second other end of the second end portions is connected to the other end and is electrically grounded.

  The collector terminal of the switching SW2f is connected to the power supply, the emitter terminal is connected to the first middle point, and the load resistor 2a and the switching SW2f are connected in parallel to the power supply. The base terminal is electrically connected to the heating circuit 2g. The detection circuit 2i connects the second middle point connecting the first end and the load resistor 2b, the third middle point connecting the load resistor 2d and the load resistor 2e, and the second end and the load resistor 2c. Each is connected to the fourth midpoint. When a signal (hereinafter referred to as a heating signal) is output from the heating circuit 2g to the base terminal of the switching SW2f, the switching SW2f is closed. Then, a current flows from the power source to the detection resistor 1a via the switch SW2f and the load resistor 2b, and power is supplied to the detection resistor 1a. The detection circuit 2i detects the voltage V2 applied to the detection resistor 1a from the second middle point. The detection circuit 2i detects the voltage V4 applied to the reference resistor 1b from the fourth middle point. Further, the detection circuit 2i detects a voltage V3 from which the voltage V1 supplied from the power supply via the switching SW2f drops by a predetermined amount due to the load resistance value of the load resistor 2d from the third middle point. On the other hand, when output of a signal from the heating circuit 2g to the base terminal of the switching SW2f is stopped, the switching SW2f is opened. Then, the current supplied from the power source to the detection resistor 1a via the switch SW2f and the load resistor 2b is cut off, and the power supply for heating the detection resistor 1a is stopped. In this case, as will be described later, since the detection resistor 1a is not connected to the power source via the load resistors 2a and 2b, a relatively weak current that does not generate heat is allowed to flow.

  The control arithmetic circuit unit 2h is electrically connected to the heating circuit 2g and is also electrically connected to the detection circuit 2i. In addition, the control arithmetic circuit unit 2 h is connected to a display device 8 arranged outside the control circuit 2. The control arithmetic circuit unit 2h includes a CPU for performing control processing, arithmetic processing, a storage device for storing various programs and data (memory such as ROM and RAM), an input circuit such as an A / D converter, an output circuit, a power circuit, etc. A microcomputer having a known structure configured to include the above functions is provided. The detection signals such as various voltage signals (V2, V4, and V3) output from the detection circuit 2i are A / D converted by the A / D converter and then input to the microcomputer. ing. The control arithmetic circuit 2h is configured to drive and control the heating circuit 2g based on a control program stored in the memory when detection start information such as a detection start signal from the outside is input to the control circuit 2. Has been. The detection start information is, for example, a signal that recognizes that the key switch of the vehicle is turned on by inserting a key into the key cylinder of the vehicle. In addition to such a recognition signal, the control circuit 2 may be turned on and the state may be the detection start information input state.

  The control arithmetic circuit section 2h detects voltages V2 and V4 applied to the detection resistor 1a and the reference resistor 1b via the detection circuit 2i, respectively. Note that when the heating signal is not output from the detection circuit 2i to the switching SW 2f by the drive control of the control arithmetic circuit unit 2h, the detection resistor 1a and the reference resistor 1b are the load resistors 2a and 2b, the load resistor, respectively. It is connected to a power source through 2c. Therefore, by setting the load resistance 2a and the load resistance 2c to a predetermined load resistance value, the detection resistor 1a and the reference resistor 1b are limited to flow a relatively weak current that does not generate heat. .

  The control arithmetic circuit unit 2h calculates the resistance values R1a and R1b of the detection resistor 1a and the reference resistor 1b based on the voltages (V2, V3, V4) detected through the detection circuit 2i. It is configured as follows. The resistance values R1a and R1b of the detection resistor 1a and the reference resistor 1b are calculated by collating with information stored in the memory or the like and stored in advance (hereinafter referred to as temperature collation information). The respective temperatures can be determined from the temperature dependence of the resistors 1a and 1b from the values R1a and R1b. The temperature verification information is a map stored in the memory (in this embodiment, for example, a map of resistance value temperature characteristics shown in a graph representing the relationship between the resistance value and temperature in FIG. 3).

  In the present embodiment, the temperature verification information will be described below as a resistance value temperature characteristic map. In FIG. 3, the horizontal axis represents temperature, and the vertical axis represents resistance values related to the detection resistor 1a and the reference resistor 1b. T0 and T represent a reference temperature and a target temperature, respectively, and ΔT represents a temperature difference between the reference temperature and the target temperature (specifically, an increase temperature in FIG. 3). ΔR represents a difference in resistance value between the resistance value R1a of the detection resistor 1a and the resistance value R1b of the reference resistor 1b at the reference temperature T0. Further, α represents the resistance value change amount obtained from the product of the resistance temperature coefficient of the detection resistor 1a and the resistance value R1a at the reference temperature T0. α × ΔT indicates a resistance value difference between the target resistance value and the reference resistance value in the detection resistor 1a. These relationships can be expressed by mathematical formulas as follows.

First, the resistance values R1a and R1b in the initial state of each resistor 1a and 1b immediately before heating the detection resistor 1a are:
R1a = V2 / {(V1-V2) / Rb}
R1b = V4 / {(V0−V4) / Rc}
And the resistance values R1a and R1b are calculated from the state where the temperature shown in FIG. 3 is the reference temperature T0. Rb and Rc are resistance values of the load resistors 2b and 2c, respectively. The relational expression of the resistance value R1a is
A relational expression of R1a = V2 / {(V0−V2) / (Ra + Rb)} may be substituted.

  Although the detection resistor 1a and the reference resistor 1b are two identical temperature resistors in this embodiment, there are actually variations between individuals, and the detection resistor 1a and the reference resistor 1b In order to compensate for the variation between individuals, a resistance value difference ΔR between the resistance value R1a and the resistance value R1b is obtained, and a correction value Offset is calculated from the following equation.

Offset = ΔR = R1a−R1b
The correction value Offset is used to correct the resistance value R1b of the resistance temperature characteristic of the reference resistor 1b, and the corrected resistance value of the resistance temperature characteristic of the reference resistor 1b is used as a detection resistor before heating. The resistance value is 1a.

Next, in the case where the detection resistor 1a is heated from the reference temperature T0 to the target temperature T, the mathematical formula for calculating the target resistance value corresponding to the target temperature T from the resistance value R1b at the reference temperature T0 is:
Target resistance value Ra = R1b + α × ΔT + Offset
It becomes.

  The correction value Offset is detected through the detection circuit 2i before heating, such as immediately before heating the detection resistor 1a, and is stored and stored in the memory in the control arithmetic circuit unit 2h. When the heating circuit 2g is driven and controlled by the control arithmetic circuit unit 2h, and the voltage V1 supplied via the switching SW is variably controlled so that the resistance value R1a of the detection resistor 1a becomes the target resistance value, The control arithmetic circuit unit 2h reads the stored correction value Offset and sets the target temperature so that the temperature difference between the reference temperature T and the target temperature T becomes a predetermined temperature difference ΔT.

In the present embodiment, the control arithmetic circuit unit 2h has a function of drivingly controlling the heating circuit 2g and variably controlling the voltage V1 as a control amount. The control arithmetic circuit 2h is preferably provided with circuits (hereinafter referred to as voltage V3 detection circuits) 2d and 2e for calculating the voltage V1 in order to feedback control the voltage V1 by PID control or the like. With this configuration, the voltage V3 detection circuits 2d and 2e detect the voltage V3 via the detection circuit 2i. Then, in the control arithmetic circuit unit 2h, the following formula V1 = V3 × (Rd + Re) / Re based on the detected voltage V3 and the resistance values Rd and Re of the load resistors 2d and 2e.
Is calculated from The resistance value during heating of the detection resistor 1a is expressed by the following formula: R1a = V2 / {(V1-V2) / Rb}
Is calculated from At this time, the reference resistor 1b is expressed by the following formula R1b = V4 / {(V0−V4) / Rc}.

  Since the voltage V1 is not constant, the resistance value R1a of the detection resistor 1a, that is, the temperature may not be calculated only by the voltage V2 applied to the detection resistor 1a. On the other hand, in the present embodiment, the voltage V3 detection circuits 2d and 2e are provided, so that the control arithmetic circuit unit 2h can detect the detection resistor 1a even when heating is performed via the detection circuit 2i. The resistance value R1a can be calculated. The resistance values Rd and Re of the load resistor 2d and the load resistor 2e are set larger than any of the resistance values of the detection resistor 1a, the reference resistor 1b, and the load resistors 2a, 2b, and 2c. In this embodiment, for example, the resistance values of the detection resistor 1a and the reference resistor 1b are set to about several tens of Ω, and the load resistance 2d and the load resistance 2e are set to about several tens of kΩ.

  Furthermore, in this embodiment, the control arithmetic circuit unit 2h includes the reference temperature compensation means S (S is a step) 201, temperature difference setting means S211 to 214, power control means S221 to S225, and power calculation means S231. And liquid level determination means S232. Detailed control processing S201 to S241 in the control arithmetic circuit unit 2h will be described later. The reference temperature compensation unit S201 has a function of compensating for a solid difference between the reference resistor 1a and the detection resistor 1b. The temperature difference setting means S211 to 214 have a function of setting the target temperature so that the temperature difference ΔT between the ambient temperature T0 and the target temperature T before heating the detection resistor 1a becomes a predetermined temperature difference. . The power control means S221 to S225 control the power supplied to the detection resistor 1a to heat or cool the detection resistor 1a to the target temperature T, and the temperature of the detection resistor 1a reaches the target temperature T Then, it has a function of controlling power so as to maintain the target temperature T. The power calculation means S231 has a function of calculating the power applied to the detection resistor 1a. The liquid level determination means S232 determines the level 3 of the engine oil 4 stored in the oil pan 5 based on the calculated power and conversion information such as a map representing the relationship between the power and the liquid level. Has a function to calculate or estimate.

  In the present embodiment, the control arithmetic circuit unit 2h has an output means S241 for notifying the vehicle occupant or the like of the liquid level 3 level detected by the liquid level determination means 232 by a notification means such as a display. . As shown in FIG. 1, the display 8 is electrically connected to the control arithmetic circuit 2h, and a display signal indicating the liquid level is output to the display 8 by the output means S241. If the output means 241 is for notifying a vehicle occupant or the like of the level 3 level of the engine oil 4, that is, the remaining amount, a display signal for display and the remaining amount are notified step by step by a sound such as a buzzer. It may be a sound signal or the like. In the following, in the present embodiment, the output means S241 outputs a display signal for visual display, and the level 3 of the engine oil 4 or the remaining amount of the engine oil 4 is displayed on a vehicle-mounted display 8 such as a meter. And the display information is transmitted to the driver and other passengers.

  Here, the detection resistor 1a and the control circuit 2 (specifically, the control arithmetic circuit unit 2h, the heating circuit 2g, and the switching SW 2f) are heating means for heating or cooling the engine oil 4 (hereinafter referred to as a heater). ). The reference resistor 1b is arranged side by side on the detection resistor 1a, and has a function of an ambient temperature detection means for detecting the ambient temperature around the detection resistor 1a.

  Next, the liquid level detection method of the present embodiment having the above-described configuration will be described with reference to FIGS. 2, 3, 4, and 5. FIG. In FIG. 5, the horizontal axis represents time, and the vertical axis represents voltage, power, and temperature (temperature of the temperature-dependent detection resistor 1a) on the upper, middle, and lower sides of FIG. Here, t0, t10, t11, t20, t21, t30, and t31 in FIG. 5 indicate time-lapse sections, t0 is an initialization section, t10 and t20 are heating sections, and t11, t21. , T31 is referred to as a target temperature maintenance interval.

  As shown in FIG. 2, in S201, the control circuit 2 (specifically, the control arithmetic circuit unit 2h) activates the detection circuit 2i before heating the detection resistor 1a (initialization interval t0 in FIG. 5). Thus, the individual difference between the detection resistor 1a and the reference resistor 1b at the temperature before the start of measurement, that is, the reference temperature T0, is measured and verified. In this embodiment, the control circuit 2 detects the individual difference between the detection resistor 1a and the reference resistor 1b at the reference temperature T0 via the detection circuit 2i, and the control arithmetic circuit unit 2h uses the resistance values R1a and R1b. Is calculated. The individual difference between the detection resistor 1a and the reference resistor 1b at the reference temperature T0 (specifically, the resistance value difference ΔR) is stored as Offset in the memory in the control arithmetic circuit 2h (Offset = ΔR). Note that the offset amount is not limited to the resistance value difference ΔR, and may be stored as a temperature difference.

  The step of calculating the resistance values R1a and R1b of the detection resistor 1a and the reference resistor 1b at the reference temperature T0 described in the control process of S201 is performed when the control process of S211 and 212 described later is executed. It may be performed simultaneously. In this case, until the control process of S214 is performed, Offset is calculated and stored in the control arithmetic circuit unit 2h.

  Thus, the reference resistor 1b can calculate or estimate the resistance value of the detection resistor 1a by correcting the offset (specifically, the resistance value difference ΔR). Even when the detection resistor 1a is being heated, by detecting the resistance value of the reference resistor 1b, the initial temperature before the detection resistor 1a is heated (see the initialization section t0 in FIG. 5) Can be grasped.

  When the detection resistor 1a is being heated, the engine oil 4 and air transfer heat generated in the heated detection resistor 1a to a relatively small amount of temperature (hereinafter referred to as the surroundings). Rise in temperature. As the heating period of the detection resistor 1a becomes longer, the temperature rises according to the elapsed time during that period. In this case (specifically, when the ambient temperature rises during heating), the reference temperature T0 is set to the target temperature by using the target resistance value of the detection resistor 1a as a reference based on the resistance value calculated by the reference resistor 1b. It is possible to heat the detection resistor 1a while maintaining the difference between the resistance value and the reference resistance value at a predetermined resistance value difference (α × ΔT in FIG. 3), that is, a predetermined temperature difference.

  In S211, the control arithmetic circuit unit 2h takes in the voltage V2 and the voltage V4 through the detection circuit 2i. At this time, since the heating signal is not output from the heating circuit 2g, the switching SW2f is open. Therefore, in S212, the resistance values R1a and R1b of the detection resistor 1a and the reference resistor 1b at the reference temperature T0 are obtained by calculating the resistance values based on the detected voltages V2 and V4.

  In S211, the voltage V2 may be detected once before heating. After the heating is started, the resistance value of the detection resistor 1a at the reference temperature T0 can be calculated based on Offset (specifically, the resistance value difference ΔR) and the resistance value R1b detected by the reference resistor 1b. (In this embodiment, R1a = ΔR + R1b as shown in FIG. 3). In this case, the operation of calculating the resistance value of the detection resistor 1a and checking the temperature from the resistance value in the control processing of S212 and S213 can be omitted.

  The control arithmetic circuit 2h stores a map as shown in FIG. 3, and in S213, the resistance values R1a and R1b calculated from the voltages V2 and V4 in S212 are correlated with the resistance values of the map and the temperature. Is converted to the temperature of the detection resistor 1a and the reference resistor 1b. In addition, since it is before heating here, the converted temperature is collated as reference temperature T0.

  In S214, the target temperature (target resistance value in this embodiment) is set from the reference temperature T0 (reference resistance in this embodiment) to a predetermined temperature difference ΔT (predetermined resistance difference α × ΔT).

  In the present embodiment, the difference between the reference temperature T0 (reference resistance) and the target temperature (target resistance value) regardless of whether the reference temperature T0 is the environmental temperature of the vehicle, the remaining amount of engine oil 4, or the running state of the vehicle. Is set to a predetermined temperature difference ΔT (predetermined resistance difference α × ΔT). In this embodiment, the target temperature (target resistance value) is calculated from the resistance value R1b of the reference resistor 1b at the reference temperature T0, and is set as target resistance value = R1b + α × ΔT + Offset.

  In S221, when the target resistance value for heating the detection resistor 1a is set in S214, a drive signal for switching to the heating circuit 2g and closing the SW2f is output. When the heating circuit 2g receives this drive signal, it outputs a heating signal to the switching SW2f and closes the switching SW2f. When the switch SW2f is closed, a current flows from the power source V0 to the detection resistor 1a via the electric load resistors 2a and 2b, and power is supplied to the detection resistor 1a. At this time, the heating voltage applied to the detection resistor 1a is detected as the voltage V2 by the detection circuit 2i in S222, and is input into the control arithmetic circuit 2h. Further, in order to calculate a voltage V1 (hereinafter referred to as a switching SW heating voltage) V1 in the switching SW2f, the voltage V3 is detected by the detection circuit 2i and input into the control arithmetic circuit 2h.

  In S223, the resistance value R1a of the detection resistor 1a during heating is obtained by calculating the resistance value based on the voltage V2 and the voltage V3 detected in S222.

  In S224, a determination is made as to whether or not the resistance value R1a of the heating detection resistor 1a calculated in S223 has reached a resistance value corresponding to the target resistance value. When the resistance value R1a of the detection resistor 1a reaches the target resistance value and becomes substantially the same value as the target resistance value, the process proceeds to S231. Conversely, if it is not substantially the same value as the target resistance value, the process proceeds to S225.

  If it is determined in S224 that the resistance value R1a of the detection resistor 1a being heated does not correspond to the target resistance value, in S225, the control calculation is performed to adjust the heating voltage V2 applied to the detection resistor 1a. The switching SW heating voltage V1 in the switching SW2f is adjusted as a control amount controlled by the circuit unit 2h. Specifically, if the resistance value R1a of the detection resistor 1a being heated is smaller than the target resistance value (target resistance value> resistance value R1a of the detection resistor 1a being heated), it is determined that the heating is insufficient. Then, a drive signal for increasing the switching SW heating voltage V1 is output from the control arithmetic circuit unit 2h to the heating circuit 2g. Conversely, if the resistance value R1a of the detection resistor 1a being heated is larger than the target resistance value (target resistance value <resistance value R1a of the detection resistor 1a being heated), it is determined that the heating is excessive. A drive signal for decreasing the switching SW heating voltage V1 is output from the control arithmetic circuit unit 2h to the heating circuit 2g. Here, the control arithmetic circuit unit 2h composed of a microcomputer includes an output circuit such as a D / A converter that can output 0 V to 5 V with an arbitrary resolution, for example, and outputs an analog voltage value. Variable output is possible. Thereby, when the voltage value of the drive signal output from the control arithmetic circuit unit 2h to the heating circuit 2g is changed, the switching SW heating voltage V1 output from the overheating circuit 2g via the switching SW can be increased or decreased. As a result, the voltage V2 applied to the detection resistor 1a, that is, the power supplied to the detection resistor 1a, can be controlled so that the detection resistor 1a reaches the target temperature (target resistance value) (FIG. 5 (see heating section t10).

  In the present embodiment, when the switching SW heating voltage V1 is adjusted in the control process of S225, it is preferable to proceed to S211. Thereby, every time the switching SW heating voltage V1 is adjusted, the target resistance value based on the resistance value R1b of the reference resistor 1b is set in the control process of S211 to S214. And the reference temperature (specifically, ambient temperature) T0 can be maintained at a predetermined temperature difference (predetermined resistance value difference), and as a result, the detection resistor 1a can be prevented from being influenced by the ambient temperature. I can plan.

  In S231, if it is determined in S224 that the resistance value R1a of the detection resistor 1a being heated is substantially equal to the target resistance value, the amount of heat for heating the detection resistor 1a and the engine oil 4 from the detection resistor 1a are determined. Further, the amount of heat deprived by the air is substantially the same, and it is determined that the temperature of the detection resistor 1a is in an equilibrium state at the target temperature. And the control arithmetic circuit part 2h maintains the predetermined switching SW heating voltage V1 without adjusting the switching SW heating voltage V1. Thereby, the voltage V2 applied to the detection resistor 1a is maintained substantially constant (see the target temperature maintaining section t11 in FIG. 5). As shown in FIG. 5, the temperature of the detection resistor 1a in the target temperature maintaining section t11 rises from the reference temperature T01 to the target temperature Ta1, and a temperature difference between the reference temperature T01 and the target temperature Ta1 is predetermined. The temperature difference ΔT can be maintained.

Further, in S231, the magnitude of the power P applied to the detection resistor 1a in this equilibrium state is expressed by the following formula: power P = V2 × I = V2 × (V1−V2) / Rb = V2 × { V3 x (Rd + Re) / Re-V2} / Rb
Is calculated from

  The control arithmetic circuit unit 2h stores a map as shown in FIG. 4, and in S232, the power calculated in S231 is converted into an oil pan based on the correlation between the map power and the liquid level 3 level. The engine oil 4 stored in 5 is converted to the level 3 level. Note that the remaining amount of the engine oil 4 may be calculated from the volume of the oil pan 5 that can store the engine oil 4 and the liquid level 3 level. For example, as shown in FIG. 4, when the power P = 0.25 W, the liquid level 3 level is calculated as 30 mm.

  In S241, a display signal is output to the meter 8 as the display information on the level 3 of the engine oil 4 calculated in S232. When the level 3 is displayed on the meter 8, an occupant such as a driver can know the remaining amount of the engine oil 4 stored in the oil pan 5.

  Here, the step of performing the control processing of S211 to S214 constitutes a temperature difference setting step. The stage of performing the control process of S221 constitutes a power supply stage. The stage of performing the control processing of S222 to S225 and S231 constitutes a power control stage. The stage of executing the control process of S231 constitutes a power calculation stage. The step of performing the control process of S232 constitutes a liquid level determination step. Of the temperature difference setting means S211 to S214, the control process of S211 to S213 and the control process of S221 to S223 of the control processes S221 to S225 detect the temperature (resistance value) of the detection resistor 1a. The temperature detecting means and the ambient temperature detecting means for detecting the temperature (resistance value) of the reference resistor 1b are configured.

  Here, a comparative example for comparison with the present embodiment will be described with reference to FIGS. 14 and 15. FIG. 14 is a configuration diagram illustrating a configuration of a liquid level detection device of a comparative example. FIG. 15 is a time chart showing an example of the liquid level detection process by the liquid level detection device of the comparative example in time series. As shown in FIG. 14, the first ends of the first ends of the detection resistor 1a are connected to a power source through a load resistor 902a, and the first other end is electrically grounded. ing. First ends of the second ends of the reference resistor 1b are connected to a power source via a load resistor 902c, and the second other end is electrically grounded. The heating circuit 902g is electrically connected so as to output a heating signal to the base terminal of the switching SW 2c. The switch SW2c and the load resistor 902a are connected in parallel to the power supply. The detection circuit 902e includes a midpoint (hereinafter referred to as a fifth midpoint) connecting the load resistor 902a and the detection resistor 1a, and a midpoint (hereinafter referred to as the first midpoint) connecting the load resistor 902c and the reference resistor 1b. 6 are called midpoints). The detection circuit 902e detects the voltage V1 supplied from the power source through the switching SW2c from the fifth middle point. This voltage V1 is a heating voltage applied to the detection resistor 1a. The detection circuit 902e detects the voltage V5 applied to the detection resistor 1a from the sixth middle point. The detection circuit 902e constitutes a comparator that compares the voltage V1 on the detection resistor 1a side with the voltage V5 on the reference resistor 1b side. The voltage control arithmetic circuit unit 902h is electrically connected to the heating circuit 902g and is also electrically connected to the detection circuit 902e. Further, the control arithmetic circuit unit 2h is connected to the display 8 arranged outside the control circuit 902. The heating circuit 2g adjusts the voltage V1 applied to the detection resistor 1a by operating the switching SW2c (interval between t0 and t1 in FIG. 15). When the switching SW 2c is closed, a voltage capable of generating heat is applied to the detection resistor 1a, and when the switching SW 2c is open, a voltage that does not cause self-heating is applied to the detection resistor 1a. In the detection circuit 902e, the threshold value is set to the upper limit side during heating, and when the voltage on the detection resistor 1a side exceeds the voltage (upper limit threshold value) on the reference resistor 1b side, the switching SW is opened and heating is stopped. A heat dissipation state is reached (section t19 in FIG. 15). In the detection circuit 902e, the upper limit threshold value V5 (H) is changed to the lower limit threshold value V5 (L), and the voltage V1 and the voltage V5 are compared. When the voltage on the detection resistor 1a side falls below the voltage (lower threshold) on the reference resistor 1b side, the switching SW is closed, heating is resumed, and a heating state is entered. Thereafter, this operation is continued. The control arithmetic circuit 2h measures the heat radiation times t19, t29, t39 during the heat radiation period, and from the change of the heat radiation times t19, t29, t39, that is, the time interval, the information held in advance (the time interval and the liquid level) The liquid level 3 level is calculated based on a map or the like representing the correlation. According to such a liquid level detection method, the liquid level 3 level cannot be detected during the heating period or the heat dissipation period when the liquid level 3 level is measured by detecting a change in the heat radiation time or the heating time. Therefore, only intermittent liquid level 3 detection can be performed.

  On the other hand, in the present embodiment, as shown in FIG. 5, the temperature of the detection resistor 1a is in equilibrium with the target temperature in the target temperature maintaining section t11. Levels can be measured repeatedly.

  In the present embodiment, as shown in FIG. 5, the liquid level 3 level can be measured in any of the target temperature maintaining sections t11, t21, and t31 while heating the detection resistor 1a. Therefore, it is possible to continuously detect the liquid level 3 level.

  Furthermore, in this embodiment, the temperature of the detection resistor 1a can be brought into an equilibrium state after heating, that is, without stopping the supply of power to the detection resistor 1a and providing a heat dissipation period.

  Furthermore, since the temperature of the detection resistor 1a is in equilibrium with the target temperature in the target temperature maintaining sections t11, t21, t31, the detection resistor 1a is changed from the target temperature Ta1 to the target temperature Ta2 during the heating period. The temperature difference can be further heated by a predetermined temperature difference ΔT, or the temperature difference from the target temperature Ta2 to the target temperature Ta3 can be cooled by a predetermined temperature difference ΔT. In this embodiment, for example, the target temperature Ta2 (target resistance Ra2) is calculated from Ra2 = R1b + 2 × α × ΔT + Offset and the resistance value R1b of the reference resistor 1b.

  Next, the operation and effect of this embodiment will be described. (1) The detection resistor 1a and the reference resistor 1b are formed so that the length in the liquid surface filling direction exceeds the range of the liquid level to be detected. ing. Further, reference resistors 1b as ambient temperature detecting means for detecting the ambient temperature around the detection resistor 1a are arranged side by side in the detection resistor 1a. Temperature difference setting means S211 to S214 for setting a target temperature T at which a difference from a temperature before heating, that is, an ambient temperature (reference temperature T0 in this embodiment) is a predetermined temperature difference, and for example, the set target temperature T is a reference. When the temperature is higher than the temperature T0, the power supplied to the detection resistor 1a is controlled to heat the detection resistor 1a to the target temperature T, and the target temperature T reaches the target temperature T when the temperature of the detection resistor 1a reaches the target temperature T. Power control means S221 to S225 for controlling the power so as to maintain the temperature T are provided. As a result, the detection resistor 1a efficiently exchanges heat between the engine oil 4 and air, and the engine oil 4 is easily deprived of heat of the detection resistor 1a and is not easily deprived of air. This makes it possible to detect the liquid level 3 that is the interface between the engine oil 4 and the air over the entire range of the liquid level 3 that is desired to be detected. Further, since the temperature of the detection resistor 1a is to be maintained at the target temperature T by the power control means power control means S221 to S225, the liquid level is changed by the change of the cooling time or resistance value during the conventional cooling, for example. As long as the target temperature T is maintained as compared with the detected one, it is possible to repeatedly measure the liquid level at three levels. Accordingly, the power control means S221 to S225 causes the detection resistor 1a to be heated or cooled to the target temperature T at which the temperature difference from the reference temperature T0, that is, the ambient temperature, becomes the predetermined temperature difference ΔT, and thereby the liquid level 3 level. Can be detected continuously. In this embodiment, for example, since the temperature of the detection resistor 1a is in equilibrium with the target temperature in the target temperature maintaining section t11, the liquid level 3 level can be repeatedly measured during the target temperature maintaining section t11. is there.

  (2) In the present embodiment, the liquid level 3 level can be measured in any of the target temperature maintaining sections t11, t21, and t31 while heating the detection resistor 1a. Therefore, continuous liquid level 3 level detection can be performed.

  (3) Furthermore, in this embodiment, the temperature of the detection resistor 1a can be brought into an equilibrium state after heating, that is, without stopping the supply of power to the detection resistor 1a and providing a heat dissipation period. .

  (4) Furthermore, in the present embodiment, the temperature of the detection resistor 1a is in equilibrium with the target temperature in each of the target temperature maintaining intervals t11, t21, t31. In addition, the temperature difference from the target temperature Ta1 to the target temperature Ta2 can be further heated by a predetermined temperature difference ΔT, or the temperature difference from the target temperature Ta2 to the target temperature Ta3 can be cooled by a predetermined temperature difference ΔT. is there.

  (5) Furthermore, in the present embodiment, it is preferable that two identical resistors are used for the detection resistor 1a and the reference resistor 1b. Although the reference resistor 1b is different from the detection resistor 1a, it has the same temperature-dependent characteristics as the detection resistor 1a. Therefore, based on the difference between the detection resistor 1a and the reference resistor 1b, Correction of a resistance value and the like related to temperature detection between both resistors 1a and 1b is facilitated.

  (6) Furthermore, in this embodiment, the power control means S221 to S225 adjust the switching SW heating voltage V1 so that the temperature of the detection resistor 1a becomes the target temperature T in S225. Then, the process returns to S211, and the target resistance value is reset again from the resistance values of the detection resistor 1a and the reference resistor 1b measured in S211 to S214. Thereby, every time the switching SW heating voltage V1 is adjusted, the target resistance value based on the resistance value R1b of the reference resistor 1b is set in the control process of S211 to S214. And the reference temperature (specifically, ambient temperature) T0 can be maintained at a predetermined temperature difference (predetermined resistance value difference), and as a result, the detection resistor 1a can be prevented from being influenced by the ambient temperature. I can plan.

  (7) Furthermore, in this embodiment, before supplying power to the detection resistor 1a, the correction value Offset based on the temperature difference between the temperature of the detection resistor 1a and the reference resistor 1b representing the ambient temperature. Based on the correction value for correcting the resistance value of the reference resistor 1b and the resistance value R1b of the reference resistor 1b corrected by the correction value Offset, the resistance value of the detection resistor 1a before power supply (Ra1 = Since the reference temperature compensation means S201 capable of estimating (R1b + Offset) is provided, the detection accuracy for detecting the temperature of the resistor for detecting the liquid level can be improved. For example, when the detection resistor 1a is maintained at the target temperature T by the power control of the power control means S221 to S225, only the temperature difference ΔT between the resistor temperature T0 and the target temperature T before heating the detection resistor 1a. In other words, a temperature difference between the temperature of the detection resistor 1a during heating including the state in which the target temperature T is maintained and the resistor temperature before heating, that is, the ambient temperature T0, is determined by a reference temperature compensation means by a predetermined temperature difference. The target temperature of the detection resistor 1a can be set to ΔT (target resistance value Ra = R1b + α × ΔT + Offset). As a result, it is possible to improve the detection accuracy for detecting the liquid level based on the power level by the liquid level determination means.

  (8) In addition, when the above configuration is expressed in the main stages of the liquid level detection method, the present embodiment is configured such that a predetermined temperature difference ΔT is added to the reference temperature T0 as the ambient temperature detected by the reference resistor 1b. A temperature difference setting step S211 to S214 in which the temperature obtained by adding or subtracting is used as a target temperature T for heating or cooling the detection resistor 1a, and for detection to heat or cool the detection resistor 1a to the target temperature T Power supply stage S221 for supplying power to the resistor 1a, and power for controlling the power supplied to the detection resistor 1a so that the target temperature T is maintained when the temperature of the detection resistor 1a reaches the target temperature T. Calculated in the control steps S222 to S225 and S231, the power calculation step S231 for calculating the magnitude of the power when the temperature of the detection resistor 1a is maintained at the target temperature T, and the power calculation step S231 And a liquid level judgment step S232 to detect the liquid surface 3 levels based on the magnitude of the power. As a result, the detection resistor 1a can detect the liquid level 3 level over the entire range of the liquid level 3 to be detected. Further, in the power supply stages S222 to S225 and S231, power is supplied to the detection resistor 1a to heat or cool the detection resistor 1a to the target temperature T, and the power control stage power supply stages S222 to S225 and In S231, when the temperature of the detection resistor 1a reaches the target temperature T, the power supplied to the detection resistor 1a is controlled so as to maintain the target temperature T. Therefore, for example, conventional cooling during transient cooling is performed. Compared to the case where the liquid level is detected by changing the time or the resistance value, if the power control steps S222 to S225 and S231 (specifically S231) are maintained at the target temperature T, the measurement of the liquid level 3 is repeated. Is possible. Therefore, in the power control steps S222 to S225 and S231, the detection resistor 1a is subjected to power control that maintains the target temperature T at which the temperature difference from the ambient temperature becomes the predetermined temperature difference ΔT, so that the liquid level 3 level is continuously increased. Can be detected.

  (9) In this embodiment, before the start of the power supply stages S222 to S225 and S231, the temperature of the detection resistor 1a and the temperature of the reference resistor 1b are detected, and correction is performed based on the difference between these temperatures. It is preferable to include a correction step S201 for correcting the temperature of the reference resistor 1b using a value (a resistance value difference Offset in the case of a resistance value difference between the resistors 1a and 1b).

  (10) In the present embodiment, the power supply stage S221 is repeated a plurality of times until reaching the power control stages S222 to S225 and S231 (specifically, S231), and the correction value Offset is set immediately before each power supply stage S221. Therefore, it is preferable that the resistance value 1b of the reference resistor 1b is corrected, and the target temperature T is corrected based on the corrected temperature. Thus, the temperature difference between the target temperature T for heating or cooling the detection resistor 1a and the ambient temperature, that is, the reference temperature T0 is always maintained at the same predetermined temperature difference ΔT. As a result, in the power control steps S222 to S225 and S231 (specifically, S231), the power can be controlled with the magnitude of power corresponding to the predetermined temperature difference ΔT.

(First modification)
When the switching SW heating voltage V1 is adjusted in the control process of S225, the method may be shifted to S214 instead of the method shifting to S211. In this case, in the control process of S222, the voltage V4 is also detected by the detection circuit 2i, and the resistance value 1b of the reference resistor 1b during heating is taken into the control arithmetic circuit unit 2h. As a result, the resistance value R1a of the detection resistor 1a during heating and the resistance value 1b of the reference resistor 1b representing the ambient temperature during heating can be simultaneously acquired by the control process of S222, and immediately after the transition to S214. It is possible to set a target resistance value.

(Second modification)
The reference temperature compensation unit S201 and the temperature difference setting unit S211 to S214 may be configured to be part of the configuration of the power control unit.

(Third Modification)
The control process of the reference temperature compensation means S201 was executed before supplying power for heating to the detection resistor 1a. However, when the control circuit 2 and the oil level sensor 1 are integrated into a module, Instead of the offset calculation before supplying the liquid level, that is, before starting the liquid level measurement, the offset amount may be stored in advance in the memory of the control arithmetic circuit unit 2h in the inspection process in the manufacturing stage.

(Fourth modification)
In this embodiment, engine oil is used as a liquid object whose liquid level 3 is detected. The liquid is not limited to engine oil but may be a medium such as fuel filled in a fuel tank. In this case, when the medium to be detected is a flammable medium such as engine oil such as lubricating oil or fuel such as gasoline, the temperature at which the medium ignites and emits smoke, and the detection resistor 1a from the operating temperature range. The temperature rise due to heating is studied and set. For example, for engine oil, the resistance value of the detection resistor 1a at room temperature (25 ° C.) is set to 20Ω, and a predetermined resistance value difference from the target resistance value is set to 4Ω. In this case, for example, the resistance temperature coefficient is increased by 0.01, and the predetermined temperature difference is increased by 20. In the case of a vehicle engine, the temperature range of engine oil is expected to change from about -30 ° C to about 130 ° C. Engine oil may emit smoke at temperatures above 160 ° C. It changes from 9Ω to 13Ω at −30 ° C. and from 41Ω to 45Ω at 130 ° C. by heating the detection resistor 1a. When the resistance is 45Ω, the temperature of the detection resistor 1a is 150 ° C. Therefore, even if there is a local temperature difference on the surface of the detection resistor 1a, there is a risk that smoke will be 160 ° C. or higher. Absent.

(Second Embodiment)
Hereinafter, other embodiments to which the present invention is applied will be described. In the following embodiments, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and description thereof will not be repeated.

  In the second embodiment, the heating circuit 2i described in the first embodiment is configured by a circuit including a switching element 2g1 such as a transistor, as shown in FIG. FIG. 6 is a circuit diagram showing an electrical configuration of the heating circuit of the control circuit according to the present embodiment.

  As shown in FIG. 6, the heating circuit 2g includes a switching element 2g1 and load resistors 2g2, 2g3, and 2g4. The collector terminal of the switching element 2g1 is connected to a power source. One end of the load resistor 2g3 is electrically connected to the control arithmetic circuit unit 2h so that the drive signal is received, and the other end is electrically connected to the base terminal of the switching element 2g1. One end of the load resistor 2g2 is connected to the emitter terminal of the switching element 2g1 and grounded, and the other end is connected to the load resistor 2g3 and the base terminal of the switching element 2g1. The load resistor 2g4 has one end connected to the collector terminal of the switching element 2g1 and the other end connected to the power source. A heating signal is output from the middle point (seventh middle point) connecting the collector terminal and the load resistor 2g4 to the switching SW 2f.

  In the operation of the heating circuit 2g having the above configuration, when the output value of the drive signal from the control arithmetic circuit 2h is increased, the heating circuit 2g outputs a heating signal to the switching SW 2f and decreases the switching SW heating voltage V1. Conversely, when the output value of the drive signal from the control arithmetic circuit 2h is reduced, the heating circuit 2g increases the switching SW heating voltage V1. Thereby, the heating circuit 2g can be formed in a simple circuit composed of the switching element 2g1.

(Third embodiment)
In the third embodiment, instead of forming the detection resistor 1a and the reference resistor 1b described in the first embodiment separately, as shown in FIG. 7, a single substrate is used. Shall be placed. FIG. 7 is an external view showing the resistor and the second resistor according to the present embodiment.

As shown in FIG. 7, the detection resistor 101a and the reference resistor 101b are arranged on a single substrate. Further, a substantially slit-shaped opening 101c is formed between the detection resistor 101a and the reference resistor 101b so as to penetrate the front surface and the back surface of the substrate. This
Heat can be blocked by the space of the substantially slit-shaped opening 101c so that the heat generated by the detection resistor 101a does not directly affect the temperature (resistance value) detected by the reference resistor 101b. Therefore, even when the detection resistor 101a is heated to the target temperature T by the power control means S221 to S225 and a temperature difference occurs with the ambient temperature (reference temperature T0), the reference resistor 101b is The ambient temperature around the detection resistor 101a can be detected independently.

  The size of the opening 101c is preferably ensured to be larger than the length of the pattern member of the detection resistor 101a (the length in the longitudinal direction of the pattern member corresponding to the vertical direction in FIG. 7). Heat transfer to the reference resistor 101b due to heating of the detection resistor 101a is alleviated. The reference resistor 101b detects the ambient temperature where the detection resistor 101a is disposed, and does not detect a temperature change of the detection resistor 101a. The ambient temperature is an average temperature at which the engine oil 4 temperature and the ambient temperature are in an equilibrium state.

(Fourth embodiment)
In the fourth embodiment, a temperature sensor 301b such as a thermistor is used instead of the reference resistor 1b described in the first embodiment, as shown in FIG. FIG. 8 is a configuration diagram showing the configuration of the liquid level detection device of the present embodiment. FIG. 9 is a time chart showing, in time series, one embodiment of the liquid level detection process by the liquid level detection apparatus of FIG.

  As shown in FIG. 8, the detection means 301 for detecting the level 3 of the engine oil 4 includes a detection resistor 1a and a thermistor (hereinafter referred to as a first thermistor) 301b. The first thermistor 301 b is disposed in the engine oil 4.

Even when configured in this way,
A condition in which the difference between the temperature of the engine oil 4 constituting the ambient temperature and the temperature of the air (atmosphere temperature) is relatively small;
Used in a medium in which the difference between the liquid temperature and the ambient temperature is small in the liquid target medium of the liquid level 3 to be detected,
Alternatively, the liquid level can be continuously measured at three levels under the above three conditions until the difference reaches a predetermined number of repetitions, for example, heating of the detection resistor 1a is repeated. In addition, in the conventional liquid level detection method, heating and heat dissipation must be alternately repeated and paused for each measurement, whereas in this embodiment, a predetermined number of repetitions, that is, a predetermined number of continuous measurements. After that, it becomes a rest.

  In the present embodiment, for example, as shown in FIG. 9, the detection resistor 1 a is periodically radiated (see the heat dissipation section t <b> 12 in FIG. 9), so that the detection resistor 1 a is in equilibrium with the ambient temperature. Set as follows. If the reference resistor 1b is present, the ambient temperature can be corrected by correcting the offset amount calculated in advance to the reference resistor 1b (addition in the first embodiment) even during the heating operation of the detection resistor 1a. Although the resistance value (temperature) of the detection resistor 1a that is in an equilibrium state is simply calculated, it cannot be easily calculated in the present embodiment. Therefore, when any of the above three conditions cannot be satisfied, the temperature at which the ambient temperature is in equilibrium is detected by the detection resistor 1a itself by radiating the detection resistor 1a.

(Fifth embodiment)
In the fifth embodiment, in addition to the first thermistor disposed in the engine oil 4 described in the fourth embodiment, as shown in FIG. 10, a second thermistor 402b disposed in the atmosphere is provided. FIG. 10 is a configuration diagram showing the configuration of the liquid level detection device of the present embodiment.

  As shown in FIG. 10, the detection means 401 for detecting the level 3 of the engine oil 4 includes a detection resistor 1a, a first thermistor 401b disposed in the engine oil 4, and an atmosphere. A second thermistor 402b is provided.

  With such a configuration, the temperature and atmospheric temperature of the engine oil 4 are detected by the first thermistor 401b and the second thermistor 402b, and weighting is performed based on the detected temperature and atmospheric temperature of the engine oil 4. It is possible to detect the ambient temperature without error by performing the correction according to the above.

  Note that there is a reference resistor 1b because of the so-called average temperature calculated by the control arithmetic circuit 2h from the first thermistor 401b and the second thermistor 402b through the detection circuit 2i and correction by weighting or the like. As compared with the case, the liquid level detection accuracy may be lowered. However, it is suitable for liquid level detection in applications where it is necessary to detect both the temperature of the liquid 4 and the ambient temperature.

(Sixth to eighth embodiments)
The applicant has confirmed that the relationship between the required power and the liquid level is a quadratic curve characteristic as shown by the solid line in FIG. In the detection resistor 901a used in this experiment, as shown in FIG. 13, the pattern member is arranged in a substantially comb-like pattern with a substantially uniform wiring pattern in a plane on which the pattern member is wired.

  On the other hand, in the sixth to eighth embodiments, as shown in FIG. 11, the pattern member is an atypical wiring pattern. FIG. 11 is a diagram showing a resistor according to the sixth to eighth embodiments, and FIGS. 11A, 11B, and 11C are diagrams showing the sixth embodiment, FIG. It is an external view of the resistor of 7th Embodiment and 8th Embodiment.

  In the detection resistor 501a according to the sixth embodiment, pattern members are arranged in a substantially comb-like shape as in the wiring pattern of FIG. 13, but as shown in FIG. Along the left-right direction between both ends of 501a, the length of the wiring pattern is long at the center side of the substrate, and the length of the wiring pattern is shortened toward the both ends.

  In the detection resistor 601a according to the seventh embodiment, a substantially comb-like wiring pattern is formed in the left-right direction as shown in FIG. 11B instead of the up-down direction in FIG. . Further, a substantially comb-like wiring pattern is formed densely in the vertical direction, and the wiring pattern is formed denser toward both end portions on the lower side of the detection resistor 601a.

  In the detection resistor 701a according to the eighth embodiment, as shown in FIG. 11C, the length of the wiring pattern is shortened toward the upper side of the substrate instead of the method of forming the wiring pattern densely in the vertical direction. The length of the wiring pattern is increased as it approaches the both ends at the bottom.

  By forming the detection resistors 501a, 601a, and 701a according to the sixth, seventh, and eighth embodiments, the relationship between the required power and the liquid level is linear as shown by the dotted line in FIG. Characteristics. As a result, the information such as a map showing the relationship between the required power and the liquid level has a linear characteristic. Therefore, the information is simplified to a simple mathematical expression or an interpolation calculation map and stored in the memory of the control arithmetic circuit 2h. I can keep it.

  Furthermore, in the stage of executing the liquid level determination means S232, the liquid level is determined based on the information indicating the linear correlation between the power held in advance and the liquid level from the magnitude of the power calculated by the power calculation means S231. When calculating the level 3 level, it becomes easy to convert the magnitude of electric power to the level 3 level. As a result, it is possible to improve the liquid level detection accuracy at the stage of performing the liquid level determination unit S232.

(Other embodiments)
In the present embodiment described above, the description has been made by applying the present invention to the detection of the level 3 of the engine oil 4 stored in the oil pan 5. However, the present invention is not limited to the detection of the level of the engine oil. The liquid level detection device and the liquid level detection method of the present invention may be applied to a device that detects a liquid level or a fuel level.

1 is a configuration diagram illustrating a configuration of a liquid level detection device according to a first embodiment of the present invention. It is a flowchart which shows the liquid level detection process performed with the control circuit in FIG. It is a graph which shows the relationship between the resistance value of a resistor in FIG. 1, and a 2nd resistor, and temperature. It is a graph which shows the relationship between the electric power used for the control processing of step 232 in FIG. 2, and a liquid level. FIG. 3 is a time chart showing one embodiment according to a liquid level detection process in FIG. 2 in time series. It is a circuit diagram which shows the electric constitution of the heating circuit of the control circuit concerning 2nd Embodiment. It is an external view which shows the resistor concerning 2nd Embodiment, and a 2nd resistor. It is a block diagram which shows the structure of the liquid level detection apparatus of 4th Embodiment. 9 is a time chart showing an example of a liquid level detection process by the liquid level detection device of FIG. 8 in time series. It is a block diagram which shows the structure of the liquid level detection apparatus of 5th Embodiment. It is a figure which shows the resistor concerning 6th-8th Embodiment, Comprising: Fig.11 (a), FIG.11 (b), and FIG.11 (c) are 6th Embodiment, 7th Embodiment. And FIG. 10 is an external view of a resistor according to an eighth embodiment. It is a typical graph explaining the effect of the resistor concerning the 6th to 8th embodiment. It is an external view which shows the resistor concerning a comparative example. It is a block diagram which shows the structure of the liquid level detection apparatus of a comparative example. It is a time chart which shows one Example of the liquid level detection process by the liquid level detection apparatus of a comparative example in time series.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Detection means 1a Detection resistor (resistor)
1b Reference resistor (second resistor, ambient temperature detection means)
2 Control circuit 2a, 2b, 2c, 2d, 2e Load resistance 2f Switching SW (switching element)
2g Heating circuit (heating unit)
2h Control arithmetic circuit part (control arithmetic part)
2i detection circuit (detection unit)
3 Liquid level 4 Engine oil (liquid)
5 Oil pan (tank)
6 Case 7 Passing hole

Claims (10)

A temperature-dependent resistor whose resistance value changes according to temperature is provided, and the resistor is arranged in a portion corresponding to the liquid level to be detected in a container in which the liquid is stored, and the specific heat of gas and liquid In the liquid level detection device that detects the liquid level using the difference between
The resistor has a length in the liquid filling direction that exceeds the range of the liquid level to be detected,
Ambient temperature detection means arranged side by side on the resistor and detecting the ambient temperature around the resistor;
A temperature difference setting means for setting a temperature obtained by adding or subtracting a predetermined temperature difference to the ambient temperature detected by the ambient temperature detection means as a target temperature for heating or cooling the resistor;
A resistor temperature detecting means for detecting the temperature of the resistor;
Controlling electric power supplied to the resistor to heat or cool the resistor to the target temperature set by the temperature difference setting means, and when the temperature of the resistor reaches the target temperature, the target temperature Power control means for controlling the power to maintain
Power calculating means for calculating the magnitude of power supplied from the power control means to the resistor;
A liquid level detection apparatus comprising: a liquid level determination means for detecting a liquid level based on the magnitude of power calculated by the power calculation means. The resistor and the ambient temperature means are arranged on a single substrate,
2. The liquid level detection device according to claim 1, wherein the substrate is provided with a substantially slit-like opening that penetrates a front surface and a back surface between the resistor and the ambient temperature detection means. The liquid level detection device according to claim 1, wherein the ambient temperature detection unit includes a first thermistor disposed in the liquid. The liquid level detection device according to claim 3, wherein the ambient temperature detection means includes a second thermistor disposed in the gas. The ambient temperature detection means includes a second resistor different from the resistor,
The liquid level detection device according to claim 1, wherein the second resistor has the same temperature-dependent characteristics as the resistor. The power control means includes
Correction means for correcting the ambient temperature detection means by a correction value based on a temperature difference between the temperature of the resistor and the ambient temperature before supplying power to the resistor;
6. The apparatus according to claim 1, further comprising: a reference temperature compensation unit configured to set the temperature of the ambient temperature detection unit corrected by the correction value to a temperature before supplying power to the resistor. The liquid level detection device according to any one of the above. The power control means includes
Before supplying power to the resistor, the resistance value of the resistor and the resistance value of the second resistor are detected, and the resistance of the second resistor is determined by a correction value based on the difference between these resistor values. Correction means for correcting the value;
The reference temperature compensation means which makes the resistance value of the 2nd resistor corrected by the correction value the resistance value before the electric power supply of the resistor is provided. Liquid level detection device. A temperature-dependent resistor whose resistance value changes according to temperature is placed in a part corresponding to the liquid level to be detected in the container in which the liquid is stored, and the difference in specific heat between the gas and the liquid is utilized. In the liquid level detection method for detecting the liquid level,
The length of the resistor in the liquid filling direction is formed so as to exceed the range of the liquid level to be detected,
Ambient temperature detection means for detecting the ambient temperature around the resistor is arranged side by side on the resistor,
A temperature difference setting step in which a temperature obtained by adding or subtracting a predetermined temperature difference to the ambient temperature detected by the ambient temperature detection means is set as a target temperature for heating or cooling the resistor;
Supplying power to the resistor to heat or cool the resistor to the target temperature; and
A power control step of controlling the power supplied to the resistor so that the target temperature is maintained when the temperature of the resistor reaches the target temperature;
A power calculation step of calculating the magnitude of power when the temperature of the resistor is maintained at the target temperature;
A liquid level detection method comprising: a liquid level determination step for detecting a liquid level based on the magnitude of electric power calculated in the power calculation step. Before the start of the power supply step, a correction step of detecting the temperature of the resistor and the temperature of the ambient temperature detection means and correcting the temperature of the ambient temperature detection means by a correction value based on the difference between these temperatures is provided. The liquid level detection method according to claim 8, wherein: The power supply stage is repeated a plurality of times until the power control stage is reached,
10. The temperature of the ambient temperature detecting means is corrected based on the correction value immediately before each power supply stage, and the target temperature is corrected based on the corrected temperature. The liquid level detection method according to 1.

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