JP5408083B2 - Liquid level detection system - Google Patents

Description

  The present invention relates to a liquid level detection system for detecting a liquid level height of a liquid stored in a container.

  2. Description of the Related Art Conventionally, a liquid level detection system including a liquid level sensor that outputs a detection current having a strength corresponding to a liquid level height of a liquid stored in a container by applying a power supply voltage by a power source is known. As one type of such a liquid level detection system, for example, a liquid level measurement system disclosed in Patent Document 1 includes a resistance type liquid level sensor, an input circuit, and a CPU. The input circuit generates a detection voltage corresponding to the intensity of the detection current output from the liquid level sensor from the power supply voltage applied by the power supply. Then, the CPU calculates the liquid level based on the detection voltage generated by the input circuit.

Japanese Patent No. 4199149

  Now, the liquid level measuring system described in Patent Document 1 is connected to a power source, and can detect the liquid level of the liquid by receiving power from the power source. The power supply voltage by this power supply is not always constant but varies. When the power supply voltage fluctuates in this way, the following problem occurs in the liquid level measurement system described in Patent Document 1.

  First, in a resistance type liquid level sensor, a varying power supply voltage is applied by a power supply. Therefore, the resistance type liquid level sensor is affected by fluctuations in the power supply voltage and cannot output a detection current having a strength corresponding to the liquid level.

  In addition, the input circuit to which the detection current output by the liquid level sensor is input generates a detection voltage corresponding to the strength of the detection current from the power supply voltage applied by the power supply. Therefore, the detection voltage generated by the input circuit includes a shift component due to the fluctuation of the power supply voltage.

  When the power supply voltage of the power supply fluctuates as described above, the liquid level measurement system cannot output an accurate detection current from the liquid level sensor and generates a detection voltage that includes a deviation in the detection circuit. Resulting in. Therefore, the liquid level measurement system described in Patent Document 1 may not be able to accurately detect the liquid level when the power supply voltage of the power supply fluctuates.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid level detection system capable of accurately detecting the liquid level height even when the power supply voltage of the power source fluctuates. That is.

  In order to achieve the above object, according to the first aspect of the present invention, the liquid level of the liquid stored in the container is detected by using the power supplied from the power source and connected to the power source. In the liquid level detection system, the sensor power supply unit that stabilizes the power supply voltage applied by the power supply, and the voltage stabilized by the sensor power supply unit is applied, so that the strength according to the liquid level is A liquid level sensor having a current control unit that outputs a detection current and a reference current having a preset strength, and a detection voltage corresponding to the detection current strength and a reference corresponding to the reference current strength A detection circuit that generates a voltage from a power supply voltage applied by a power supply, a correction unit that corrects the detection voltage generated by the detection circuit using a reference voltage, and a detection voltage corrected by the correction unit. , The liquid level detection system comprising a calculating means for calculating a height of the liquid surface.

  According to the present invention, in the liquid level sensor, the power supply voltage applied by the power supply is stabilized by the sensor power supply unit. In this way, since the stabilized voltage is applied, the current control unit is less susceptible to the influence of fluctuations in the power supply voltage, so that a detection current having a strength corresponding to the liquid level can be output accurately. It becomes like this.

  The current control unit outputs a reference current having a preset strength. As described above, a voltage stabilized by the sensor power supply unit is applied to the current control unit. Therefore, similarly to the detection current, the strength of the reference current is hardly affected by fluctuations in the power supply voltage. In addition, the strength of the reference current is predetermined. As described above, the reference current output from the current control unit is an accurate and constant current.

  The detection circuit to which the detection current and the reference current are input generates a detection voltage corresponding to the intensity of the detection current and a reference voltage corresponding to the intensity of the reference current from the power supply voltage applied by the power supply. As described above, since the reference current is accurate and constant, the fluctuation occurring in the reference voltage is substantially caused by the fluctuation of the power supply voltage. Therefore, the correction means can estimate the deviation component due to the fluctuation of the power supply voltage included in the detection voltage generated by the detection circuit from the fluctuation of the reference voltage. As described above, the correction unit can remove the component of the deviation caused by the fluctuation of the power supply voltage included in the detection voltage from the detection voltage by correcting using the reference voltage.

  The liquid level detection system having the above configuration can output an accurate detection current from the liquid level sensor, and can correct a deviation in detection voltage generated in the detection circuit by the correction means. Therefore, the liquid level detection system can accurately detect the liquid level even if the power supply voltage of the power supply fluctuates.

  According to the second aspect of the present invention, the current control unit converts the weakest current among the currents output as the detection current and the strongest current among the currents output as the detection current into a pair of reference currents. The detection circuit acquires a high voltage reference voltage having a large value from the pair of reference voltages and a low voltage reference voltage having a small value from the pair of reference voltages from the detection circuit, and obtains the low voltage reference voltage from the high voltage reference voltage. A ratio of a value obtained by subtracting the low-voltage reference voltage from the detection voltage to a value obtained by subtracting the value is obtained, and the calculation means calculates the liquid level height from the ratio based on the detection voltage obtained by the correction means. .

  In the present invention, when the detection voltage rises and falls due to the fluctuation of the power supply voltage, the high voltage reference voltage having a large value among the pair of reference voltages and the low voltage reference voltage having a small value among the pair of reference voltages are similarly applied. Go up and down. Therefore, even when the power supply voltage fluctuates, the ratio of the value obtained by subtracting the low-voltage reference voltage from the detection voltage to the value obtained by subtracting the low-voltage reference voltage from the high-voltage reference voltage is difficult to change. In this way, by correcting the detection voltage so as to represent the ratio, the correction unit can reliably remove the component of deviation caused by the fluctuation of the power supply voltage included in the detection voltage from the detection voltage. Therefore, the liquid level detection system can detect the liquid level height more accurately even if the power supply voltage of the power supply fluctuates.

  In the invention according to claim 3, the current control unit sequentially outputs a pair of reference currents, the detection circuit sequentially generates a pair of reference voltages corresponding to the strength of the pair of reference currents, A pair of high voltage reference voltage and low voltage reference voltage sequentially generated by the detection circuit is acquired, and a ratio of a value obtained by subtracting the low voltage reference voltage from the detection voltage to a value obtained by subtracting the low voltage reference voltage from the high voltage reference voltage is obtained. It is characterized by that.

  When the current control unit outputs a pair of reference currents as in the present invention, these reference currents are preferably output in order from the current control unit. Accordingly, the detection circuit can sequentially generate the reference voltages corresponding to the strengths of the pair of reference currents. Thereby, the time from when one of the pair of reference voltages is generated to when the other is generated can be shortened. Therefore, since fluctuations in the power supply voltage between the generation of one of the pair of reference voltages and the generation of the other can be suppressed, the pair of reference voltages is generated from the power supply voltages having substantially the same potential. obtain. As described above, the value used by the correcting means for correcting the detected voltage, and the value obtained by subtracting the low voltage reference voltage from the high voltage reference voltage can be accurate. Therefore, the correction unit can accurately remove the component of the deviation caused by the fluctuation of the power supply voltage included in the detection voltage from the detection voltage. Therefore, the liquid level detection system can detect the liquid level height more accurately even if the power supply voltage of the power supply fluctuates.

  In the invention according to claim 4, the current control unit outputs the reference current by starting the application of voltage by the sensor power supply unit with the start of power supply to the liquid level detection system by the power supply, The detection circuit outputs a detection current, the detection circuit generates a reference voltage, and then generates a detection voltage. The correction unit corrects the detection voltage with a reference voltage generated before the detection voltage. To do.

  In general, the power supply voltage may fluctuate greatly even when power is not supplied to the liquid level detection system. Therefore, according to the present invention, with the start of power supply by the power source, the current control unit that has started applying the voltage by the sensor power source unit is configured to output the detection current after first outputting the reference current. Thereby, in the detection circuit, the latest reference voltage reflecting the power supply voltage after starting the power supply is first generated. Therefore, when correcting the detection voltage, the correction unit can use the latest reference voltage acquired before the detection voltage for correction. As described above, by using the reference voltage that reflects the power supply voltage after the power supply is started, the correction unit detects the component of the deviation caused by the fluctuation of the power supply voltage included in the detection voltage. Can be accurately removed from the voltage. Therefore, even when the power supply voltage of the power supply greatly fluctuates while no current is supplied to the liquid level detection system, the liquid level detection system can accurately detect the liquid level.

  According to the fifth aspect of the present invention, the current control unit outputs a reference current for each preset period, and the correction means is generated by the detection circuit according to the strength of the reference current output for each period. The detection voltage generated by the detection circuit after the reference voltage is corrected using the reference voltage.

  In the configuration of the present invention, the power supply voltage continues to fluctuate even while the detection of the liquid level by the liquid level detection system is continued. Therefore, by using a current control unit that outputs a reference current for each preset period, the correction unit can acquire a reference voltage generated from the latest power supply voltage. Then, by correcting the detection voltage using the latest reference voltage, the correction unit can accurately remove the deviation component caused by the fluctuation of the power supply voltage included in the detection voltage from the detection voltage. Therefore, the liquid level detection system can continue to accurately detect the liquid level even in a situation where the liquid level is continuously used.

It is a circuit diagram which shows the electrical constitution of the liquid level detection system by one Embodiment of this invention. It is a figure for demonstrating the structure of a liquid level sensor, Comprising: (a) It is a figure which shows the mechanical structure of a liquid level sensor, (b) It is a figure which shows the electrical structure of a liquid level sensor. It is a timing chart which shows transition of current outputted from a current control part. It is a flowchart which shows the process which a meter control circuit calculates a liquid level height.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a circuit diagram showing an electrical configuration of a liquid level detection system 100 according to an embodiment of the present invention. FIG. 2 is a diagram showing a mechanical configuration and an electrical configuration of the liquid level sensor 20. The liquid level detection system 100 detects the liquid level height of the fuel stored in the fuel tank 90 by the liquid level sensor 20 installed in the fuel tank 90 of the vehicle, and the fuel provided in the combination meter 80. The detection result is output toward the total 60.

  As shown in FIG. 1, the liquid level detection system 100 includes the liquid level sensor 20 described above, a detection circuit 50 provided in a combination meter, a meter control circuit 40, and the like. In addition, the liquid level detection system 100 is connected to the meter power supply circuit 10, the fuel gauge 60, and the ground circuit 70 provided in the combination meter 80.

  As shown in FIGS. 1 and 2, the liquid level sensor 20 includes a float 21, a magnet holder 23, a float arm 24, and a housing 25.

  The float 21 is formed in a rectangular parallelepiped shape with a small thickness by a material having a small specific gravity such as foamed ebonite. The float 21 can be floated on the fuel surface by being formed of a material having a specific gravity smaller than that of the fuel. In the float 21, a through-hole for externally fitting to the float arm 24 is formed so as to pass through the center of gravity of the float 21.

  The magnet holder 23 is formed into a cylindrical shape with, for example, polyacetal (POM) resin having excellent oil resistance, solvent resistance, and mechanical properties. The magnet holder 23 is rotatably supported by the housing 25 by a bearing portion formed on the inner peripheral surface thereof. A cylindrical magnet exhibiting ferromagnetism is embedded in the magnet holder 23 by insert molding. The magnet is embedded so that its central axis coincides with the central axis of the magnet holder, and rotates integrally with the magnet holder 23.

  The float arm 24 is formed of a round bar-shaped core material made of a metal material such as stainless steel. The float 21 is held at one end of both ends of the float arm 24. The other end of the float arm 24 is held by a magnet holder 23.

  The housing 25 is formed into a rectangular plate shape using polyphenylene sulfide (PPS) resin or the like that is not affected by an organic solvent such as fuel and does not decrease in strength even at high temperatures. The housing 25 is attached to a wall surface of a fuel pump module or the like with its longitudinal direction oriented in the vertical direction, and the liquid level sensor 20 is fixed to the fuel tank 90.

  With the above configuration, the reciprocating motion of the float 21 that moves up and down following the fuel level by the float arm 24 is converted into a rotational motion and transmitted to an integral element composed of the float arm 24 and the magnet holder 23. Therefore, the magnet holder 23 follows the liquid level of the fuel stored in the fuel tank 90 and rotates relative to the housing 25.

  The liquid level sensor 20 includes a power supply terminal 31, a sensor power supply unit 32, a magnetic sensor unit 33, an EEPROM 34, a current control unit 35, and an output terminal 36 as an electrical configuration.

  The power supply terminal 31 is connected to the meter power supply circuit 10 via the meter control circuit 40. For example, a power supply voltage Ve of 5 V is applied to the power supply terminal 31 from the meter power supply circuit 10.

  The sensor power supply unit 32 is connected to the power supply terminal 31 and stabilizes the power supply voltage Ve applied by the meter power supply circuit 10. The sensor power supply unit 32 is connected to the magnetic sensor unit 33, the EEPROM 34, and the current control unit 35. The sensor power supply unit 32 applies a stabilized voltage to the magnetic sensor unit 33, the EEPROM 34, and the current control unit 35.

  The magnetic sensor unit 33 includes a magnet embedded in the magnet holder 23 and a Hall element embedded in the housing 25. The Hall element is located on the inner peripheral side of a cylindrical magnet embedded in the magnet holder 23. In the above configuration, as the liquid level of the fuel moves up and down, the magnet rotates integrally with the magnet holder 23, whereby the density of the magnetic flux passing through the Hall element changes. The Hall element is connected to the sensor power supply unit 32, and a voltage is applied by the sensor power supply unit 32. The Hall element to which the voltage is applied converts the change in the density of the magnetic flux passing through the Hall element into an electrical signal and outputs it to the EEPROM 34.

  The EEPROM 34 is a storage medium for storing various information related to the liquid level sensor 20. The EEPROM 34 stores information about output characteristics that define what current the current control unit 35 outputs in response to the electrical signal output by the magnetic sensor unit 33. The EEPROM 34 corrects or converts the electrical signal output from the magnetic sensor unit 33 as appropriate and outputs it to the current control unit 35.

  The current control unit 35 is connected to the sensor power supply unit 32 and the output terminal 36. The electric signal output from the magnetic sensor unit 33 is input to the current control unit 35 via the EEPROM 34. The current control unit 35 outputs a detection current Ix having a strength corresponding to the liquid level when a voltage stabilized by the sensor power supply unit 32 is applied.

  The output terminal 36 is connected to the ground circuit 70 via the meter control circuit 40. The detected current Ix output by the current control unit 35 is input to the meter control circuit 40 through the output terminal 36.

  The detection circuit 50 generates a detection voltage corresponding to the intensity of the detection current Ix output from the liquid level sensor 20 from the power supply voltage Ve applied by the meter power supply circuit 10. The detection circuit 50 includes a wiring 51, a wiring 52, a resistor 53, a wiring 54, a low-pass filter circuit 55, a wiring 56, and a resistor 57.

  The wiring 51 connects the meter power supply circuit 10 and the power supply terminal 31. The wiring 52 connects the ground circuit 70 and the output terminal 36. The resistor 53 is a passive element having a predetermined electric resistance, and is provided on the wiring 51. The wiring 54 connects the meter control circuit 40 to the voltage detection unit 58 located between the resistor 53 and the power supply terminal 31 in the wiring 51.

  The low-pass filter circuit 55 is provided in the wiring 54 and prevents a current in a band higher than a predetermined frequency from being input to the meter control circuit 40. The low pass filter circuit 55 includes a resistor 55a, a wiring 55b, a capacitor 55c, and the like. The resistor 55 a is provided on the wiring 54. The wiring 55 b connects between the resistor 55 a and the meter control circuit 40 and the wiring 52 in the wiring 54. The capacitor 55c is a passive element having a predetermined capacitance, and is provided on the wiring 55b.

  The wiring 56 connects the voltage detection unit 58 and the low-pass filter circuit 55 in the wiring 54 to the wiring 52. The resistor 57 is a passive element having a predetermined electric resistance, and is provided on the wiring 56.

  In the detection circuit 50 configured as described above, the detection current Ix output from the liquid level sensor 20 flows to the ground circuit 70 via the wiring 52. In the detection circuit 50, the detection voltage Vx in the voltage detection unit 58 changes according to the intensity of the detection current Ix input from the liquid level sensor 20 to the detection circuit 50. As described above, since the intensity of the detection current Ix changes according to the liquid level of the fuel stored in the fuel tank 90, the height of the detection voltage Vx in the voltage detection unit 58 is also equal to the liquid level. Will change accordingly. The detection voltage Vx generated in the voltage detection unit 58 is acquired by the meter control circuit 40 via the wiring 54 and the low-pass filter circuit 55.

  The meter control circuit 40 is configured by a microcomputer or the like for performing various calculations. Based on the detected voltage Vx, the meter control circuit 40 calculates a value indicating the liquid level, and thus the remaining amount of fuel. Specifically, the meter control circuit 40 calculates an average value of a plurality of detection voltages Vx acquired during a predetermined time. The meter control circuit 40 controls the fuel gauge 60 based on the calculation result, and causes the fuel gauge 60 to form a display for informing the viewer of the remaining amount of fuel.

  The meter power supply circuit 10 is connected to a battery or the like mounted on the vehicle, and power is supplied from the battery. The meter power supply circuit 10 is connected to the liquid level sensor 20, the meter control circuit 40, the detection circuit 50, and the like. The meter power supply circuit 10 converts the power supplied from the battery into a form suitable for the liquid level sensor 20, the meter control circuit 40, the detection circuit 50, and the like, and supplies the power to these elements 20, 40, 50, and the like.

  The fuel gauge 60 forms a display for informing the viewer of the remaining amount of fuel stored in the fuel tank 90. The fuel gauge 60 includes a dial (not shown) on which numerals and letters are formed, a pointer indicating the number (not shown), a stepping motor (not shown) for rotating the pointer, and the like. The stepping motor rotates the pointer based on a signal input from the meter control circuit 40, specifically, a digital pulse. As a result, a display indicating the remaining amount of fuel is formed on the fuel gauge 60.

  The ground circuit 70 is grounded to the body of the vehicle, for example. The ground circuit 70 is connected to the detection circuit 50, the meter control circuit 40, and the like, and drops charges input from the detection circuit 50 and the meter control circuit 40 to the vehicle body and the like.

  Next, the operation in which the liquid level detection system 100 having the above configuration detects the liquid level will be described in detail.

  First, the operation of the liquid level sensor 20 will be described with reference to FIGS. 3 and 2. FIG. 3 is a timing chart showing the transition of the current output from the current control unit 35. When the application of the power supply voltage Ve from the meter power supply circuit 10 to the liquid level sensor 20 is started, the sensor power supply unit 32 starts to apply a stabilized voltage to the magnetic sensor unit 33, the EEPROM 34, and the current control unit 35. . Thereby, the detection of the liquid level by the liquid level sensor 20 and the output of the current by the current control unit 35 are started from time t0.

The EEPROM 34 outputs an electric signal to the current control unit 35 so that preset reference currents I _Low and I _Hi are output from the current control unit 35 after application of voltage by the sensor power supply unit 32 is started. . Thereby, the current control unit 35 sequentially outputs a pair of reference currents I _Low and I _Hi . The current control unit 35 outputs the reference current I _Low from time t0 when application of voltage is started by the sensor power supply unit to time t1 when a preset time T1 has elapsed. The intensity of the reference current I _Low is the same as the weakest current among the currents output as the detection current Ix. From time t1 to time t2 when a preset time T2 has elapsed, the current control unit 35 outputs the reference current I _Hi . The intensity of the reference current I _Hi is the same as the strongest current among the currents output as the detection current Ix.

The EEPROM 34 outputs an electrical signal to the current control unit 35 so that the detected current Ix is output from the current control unit 35 after the time t2. The EEPROM 34 appropriately corrects or converts the electric signal based on the liquid level input from the magnetic sensor unit 33 and outputs the electric signal to the current control unit 35. As described above, the current control unit 35 sequentially outputs the reference current I _Low and the reference current I _Hi, and then outputs the detection current Ix from time t2 to time t3. This time t3 is a time when a preset time T0 has elapsed from the time t0.

The EEPROM 34 outputs an electric signal to the current control unit 35 so as to output the reference currents I _Low and I _Hi again after the elapse of time t3. By such an operation of the EEPROM 34, the current control unit 35 sequentially outputs the reference currents I _Low and I _Hi and the detection current Ix for each preset period T0.

Next, the reference currents I _Low and I _{Hi and the} detection current Ix as described above are input from the liquid level sensor 20 to the detection circuit 50, whereby the voltage in the voltage detection unit 58 of the detection circuit 50 changes. explain.

The reference current I _Low is input from the liquid level sensor 20 to the detection circuit 50 from time t0 to time t1. The voltage of the voltage detector 58 at this time is the low voltage reference voltage V _Low . The reference current I _Hi is input from the liquid level sensor 20 to the detection circuit 50 from time t1 to time t2. At this time, the voltage of the voltage detector 58 becomes a high voltage reference voltage V _Hi higher than the low voltage reference voltage V _Low .

As described above, the detection circuit 50 generates the low voltage reference voltage V _Low and the high voltage reference voltage V _Hi corresponding to the strengths of the reference currents I _Low and I _Hi from the power supply voltage Ve applied by the meter power supply circuit 10. . Then, the detection voltage Vx is generated from time t2 to time t3 after the low voltage reference voltage V _Low and the high voltage reference voltage V _Hi are generated in order.

Next, a process in which the meter control circuit 40 acquires the reference voltages V _Low and V _{Hi and the} detection voltage Vx and corrects and calculates the liquid level will be described with reference to FIG. The process shown in the flowchart of FIG. 4 is performed by the meter control circuit 40 when power supply from the meter power supply circuit 10 to the meter control circuit 40 is started, and is repeatedly performed until the current supply is stopped.

In S101, counting of elapsed time t from time t0 is started, and the process proceeds to S102. This time t0 is the time when the power supply by the meter power supply circuit 10 is started as described above. In S102, the voltage generated in the voltage detection unit 58 of the detection circuit 50 is acquired via the low-pass filter circuit 55. The voltage in the voltage detector 58 changes in order from the low voltage reference voltage V _Low to the high voltage reference voltage V _Hi . In S102, the low voltage reference voltage V _Low and the high voltage reference voltage V _Hi are acquired in order, and the process proceeds to S103. Here, each of the low-voltage reference voltage V _Low and the high-voltage reference voltage V _Hi may be acquired by the meter control circuit 40 a plurality of times, and may be stored in the meter control circuit 40 as an average value thereof.

In S103, it acquires the detected voltage Vx, which is generated in the voltage detection unit 58 after the high reference voltage _{V Hi.} In S103, the detection voltage Vx is acquired a plurality of times, and an average value thereof is calculated. Then, the process proceeds to S104.

In S104, the detection voltage Vx acquired in S103 is corrected using the low voltage reference voltage V _Low and the high voltage reference voltage V _Hi acquired in S102, and the process proceeds to S105. Specifically, a ratio S of a value obtained by subtracting the _low- voltage reference voltage V _Low from the detection voltage Vx with respect to a value obtained by subtracting the _low- voltage reference voltage V _Low from the high-voltage reference voltage V _{Hi is obtained} from Equation 1 below.

Ｓ１０５では、Ｓ１０４において算出された検出電圧Ｖｘに基づく比率Ｓから、液面の高さ、ひいては燃料残量を示す値を演算し、燃料計６０に出力する。そして、演算された値に基いて、燃料計６０を制御し、当該燃料残量を示す表示を形成させ、Ｓ１０６に進む。

In S <b> 105, a value indicating the height of the liquid level and, in turn, the remaining amount of fuel is calculated from the ratio S based on the detection voltage Vx calculated in S <b> 104 and output to the fuel gauge 60. Then, based on the calculated value, the fuel gauge 60 is controlled to form a display indicating the remaining fuel amount, and the process proceeds to S106.

  In S106, it is determined whether or not the elapsed time t at which the counting was started in S102 has passed a preset time t3. If it is determined in S106 that the elapsed time t has not passed the time t3, the process returns to S103. On the other hand, when it is determined in S106 that the elapsed time t has passed the time t3, the process proceeds to S107.

In S107, after the elapsed time t is reset, the counting is started again, and the process returns to S102. Then, the processing from S102 to S107 is repeated. Thereby, the meter control circuit 40 corrects the detection voltage Vx after the reference voltage by using the reference voltages V _Low and V _Hi generated by the detection circuit 50 every preset period T0.

  In the first embodiment described so far, in the liquid level sensor 20, the power supply voltage Ve applied by the meter power supply circuit 10 is stabilized by the sensor power supply unit 32. In this way, since the stabilized voltage is applied, the current control unit 35 becomes less susceptible to the influence of the fluctuation of the power supply voltage Ve. Therefore, the detected current Ix having a strength that accurately corresponds to the liquid level height. Can be output.

The current control unit 35 is applied with a voltage stabilized by the sensor power supply unit 32. Therefore, similarly to the detection current Ix, the strength of the reference current I _Low is hardly affected by fluctuations in the power supply voltage Ve. In addition, the strengths of the reference currents I _Low and I _Hi are determined in advance. As described above, these reference currents I _Low and I _Hi become accurate and constant currents.

The detection circuit 50 to which the detection current Ix and the reference currents I _Low and I _Hi are input generates the detection voltage Vx and the reference voltages V _Low and V _Hi from the power supply voltage Ve. As described above, since the reference currents I _Low and I _Hi have an accurate and constant strength, fluctuations occurring in the reference voltages V _Low and V _Hi are substantially caused by fluctuations in the power supply voltage Ve. Become. Therefore, the meter control circuit 40 can estimate the component of deviation caused by the fluctuation of the power supply voltage Ve included in the detection voltage Vx generated by the detection circuit 50 from the fluctuation of the reference voltages V _Low and V _Hi . As described above, the meter control circuit 40 corrects the reference voltage V _Low and V _Hi using the reference voltage V _Low and V _Hi so that the component of the deviation caused by the fluctuation of the power supply voltage Ve included in the detection voltage Vx is detected from the detection voltage Vx. Can be removed.

  The liquid level detection system 100 configured as described above can output an accurate detection current Ix from the liquid level sensor 20 and can also correct the deviation of the detection voltage Vx generated in the detection circuit 50 by the meter control circuit 40. . Therefore, the liquid level detection system 100 can accurately detect the liquid level even if the power supply voltage Ve of the meter power supply circuit 10 fluctuates.

In addition, in the first embodiment, when the detection voltage Vx rises and falls due to the fluctuation of the power supply voltage Ve, the high voltage reference voltage V _Hi and the low voltage reference voltage V _{Low rise} and _{fall in the} same manner. Therefore, even when the power supply voltage Ve fluctuates, the ratio S of the value obtained by subtracting the _low- voltage reference voltage V _Low from the detection voltage Vx to the value obtained by subtracting the _low- voltage reference voltage V _Low from the high-voltage reference voltage V _Hi is: Hard to change. In this way, by correcting the detection voltage Vx so as to be represented by the ratio S, the meter control circuit 40 converts the component of deviation caused by the fluctuation of the power supply voltage Ve included in the detection voltage Vx into the detection voltage Vx. Can be reliably removed from. Therefore, the liquid level detection system 100 can accurately detect the liquid level even if the power supply voltage Ve of the meter power supply circuit 10 fluctuates.

In the first embodiment, the reference currents I _Low and I _Hi are sequentially output from the liquid level sensor 20, so that the detection circuit 50 can generate the reference voltages V _Low and V _Hi in order. As a result, the time from when the low voltage reference voltage V _Low is generated to when the high voltage reference voltage V _Hi is generated can be shortened. Therefore, since the fluctuation of the power supply voltage Ve from when the low voltage reference voltage V _Low is generated to when the high voltage reference voltage V _Hi is generated can be suppressed, the low voltage reference voltage V _Low and the high voltage reference voltage V _Hi are substantially equal to each other. In other words, the power source voltage Ve can be generated from the same potential.

As described above, the value obtained by subtracting the _low- voltage reference voltage V _Low from the high-voltage reference voltage V _Hi and the ratio S can be accurate. Therefore, the meter control circuit 40 can accurately remove the deviation component due to the fluctuation of the power supply voltage Ve included in the detection voltage Vx from the detection voltage Vx. Therefore, the liquid level detection system 100 can accurately detect the liquid level even if the power supply voltage Ve of the power source fluctuates.

Furthermore, the power supply voltage Ve in the first embodiment may greatly fluctuate even during the time when power is not supplied to the liquid level detection system 100 due to natural discharge generated in the battery. Therefore, when a voltage is applied by the sensor power supply unit 32, the liquid level sensor 20 is configured to output the detection current Ix after first outputting the reference current I _Low and the reference current I _Hi in order. As a result, the detection circuit 50 first generates the latest high-voltage reference voltage V _Hi and low-voltage reference voltage V _Low reflecting the power supply voltage Ve after the start of power supply. Therefore, when correcting the detection voltage Vx, the meter control circuit 40 uses the latest high-voltage reference voltage V _Hi and low-voltage reference voltage V _Low acquired before the detection voltage Vx to calculate the ratio S for correction. Can be used.

As described above, the meter control circuit 40 uses the high-voltage reference voltage V _Hi and the low-voltage reference voltage V _Low that reflect the power supply voltage Ve after the power supply is started, so that the meter control circuit 40 includes the power supply included in the detection voltage Vx. The shift component due to the fluctuation of the voltage Ve can be accurately removed. Therefore, even when the power supply voltage Ve fluctuates greatly while no current is supplied to the liquid level detection system 100, the liquid level detection system 100 can accurately detect the liquid level height.

In addition, in the first embodiment, the power supply voltage Ve continues to fluctuate even while the detection of the liquid level by the liquid level detection system 100 is continued. Therefore, by using the liquid level sensor 20 that outputs the reference currents I _Low and I _Hi for each preset period T0, the meter control circuit 40 allows the high-voltage reference voltage V _Hi generated from the latest power supply voltage Ve and The low voltage reference voltage V _Low can be acquired. Then, by correcting the detection voltage Vx using the latest high-voltage reference voltage V _Hi and the low-voltage reference voltage V _Low , the meter control circuit 40 causes the deviation due to the fluctuation of the power supply voltage Ve included in the detection voltage Vx. Can be accurately removed from the detected voltage Vx. Therefore, the liquid level detection system 100 can continue to accurately detect the liquid level height even under continuous use conditions.

  In the present embodiment, the meter power supply circuit 10 corresponds to the “power supply” described in the claims, the fuel tank 90 corresponds to the “container” described in the claims, and the fuel corresponds to the claims. The meter control circuit 40 corresponds to “correction means” and “calculation means” described in the claims.

(Other embodiments)
As mentioned above, although one embodiment by the present invention was described, the present invention is not interpreted limited to the above-mentioned embodiment, and can be applied to various embodiments within the range which does not deviate from the gist.

In the above embodiment, the meter control circuit 40 calculates the ratio S from the high voltage reference voltage V _Hi , the low voltage reference voltage V _Low , and the detection voltage Vx, thereby causing the fluctuation of the power supply voltage Ve included in the detection voltage Vx. The correction was made to remove the deviation. However, as long as the detection voltage Vx is corrected using the reference voltage, the correction method is not limited to that described in the above embodiment. For example, the meter control circuit obtains a difference between the current reference voltage generated in the detection circuit and the reference voltage stored in advance. Then, the meter control circuit subtracts or adds this difference to the detection voltage Vx, thereby removing a deviation component caused by fluctuations in the power supply voltage Ve included in the detection voltage Vx. Even in the liquid level detection system including the meter control circuit that performs the correction as described above, the accuracy of detection of the liquid level can be improved.

In the above embodiment, the pair of reference currents I _Low and I _Hi output from the current control unit 35 of the liquid level sensor 20 are the weakest and strongest of the currents output as the detection current Ix, respectively. It was set to be the same. However, the strength of the current output from the current control unit as the reference current may be arbitrarily set regardless of the strength of the detection current Ix. If a liquid level sensor that outputs a pair of reference currents having different strengths is used, the meter control circuit can calculate the ratio S based on the detection voltage Vx.

In the above embodiment, when calculating the ratio S, the meter control circuit 40 uses a value obtained by subtracting the _low- voltage reference voltage V _Low from the detection voltage Vx. However, the meter control circuit, a value obtained by subtracting the detected voltage Vx from the high reference voltage V _Hi, divided by a value obtained by subtracting the low reference voltage V _Low from the high reference voltage V _Hi, it calculates the ratio based on the detected voltage Vx May be.

In the above embodiment, the liquid level sensor 20 sequentially outputs a pair of reference currents I _Low and I _Hi after the application of the power supply voltage Ve to the liquid level sensor 20 is started. However, the timing at which the plurality of reference currents are output does not have to be in the order as in the above embodiment, and does not have to be immediately after the voltage is applied. The timing at which the reference voltage is output may be set as appropriate.

In the above embodiment, the reference currents I _Low and I _Hi are output every period T0. However, the liquid level sensor may output the reference current only immediately after the voltage application is started. Alternatively, the liquid level sensor may output a reference current based on a command from the meter control circuit.

  In the said embodiment, the liquid level sensor 20 of the form which detects a liquid level height using the float 21 which floats on the liquid was used. However, for example, an ultrasonic liquid level sensor or an optical liquid level sensor may be used as long as the reference current can be output. An ultrasonic or optical liquid level sensor means that the ultrasonic or infrared light emitted toward the liquid level is reflected on the liquid level and the time until the liquid level sensor returns to the liquid level sensor is measured. It is a sensor that detects the surface height.

  The present invention has been described based on the example applied to the liquid level detection system 100 that detects the liquid level of the fuel stored in the fuel tank 90 of the vehicle. However, the application target of the present invention is the liquid level of the fuel. It is not limited to height detection. The present invention may be applied to a liquid level detection system in a container such as other fluids mounted on a vehicle, such as brake fluid, engine cooling water, and engine oil. Furthermore, the present invention may be applied to a liquid level detection system in a container provided in various consumer devices and various transport machines, not limited to vehicles.

10 meter power supply circuit (power supply), 20 liquid level sensor, 21 float, 23 magnet holder, 24 float arm, 25 housing, 31 power supply terminal, 32 sensor power supply section, 33 magnetic sensor section, 34 EEPROM, 35 current control section, 36 Output terminal, 40 meter control circuit (correction means, calculation means), 50 detection circuit, 51, 52, 54, 55b, 56 wiring, 53, 55a, 57 resistor, 55 low-pass filter circuit, 55c capacitor, 58 voltage detection unit , 60 Fuel meter, 70 Ground circuit, 80 Combination meter, 90 Fuel tank (container), 100 Liquid level detection system, Ix detection current, I _Hi , I _Low reference current, Ve power supply voltage, Vx detection voltage, V _Hi high voltage reference Voltage, V _{Low Low} voltage reference voltage

Claims (5)

A liquid level detection system that detects the liquid level of the liquid stored in the container by using power supplied from the power source and connected to the power source,
A sensor power supply that stabilizes the power supply voltage applied by the power supply, and a voltage that is stabilized by the sensor power supply is applied to output a detection current having a strength corresponding to the liquid level. A liquid level sensor having a current control unit that outputs a reference current having a preset strength, and
A detection circuit that generates a detection voltage according to the intensity of the detection current and a reference voltage according to the intensity of the reference current from the power supply voltage applied by the power supply;
Correction means for correcting the detection voltage generated by the detection circuit using the reference voltage;
Based on the detected voltage corrected by the correcting means, calculating means for calculating the height of the liquid level;
A liquid level detection system comprising: The current control unit outputs the weakest current among the currents output as the detection current and the strongest current among the currents output as the detection current, as a pair of the reference currents,
The detection circuit generates a pair of reference voltages according to the strength of the pair of reference currents from the power supply voltage applied by the power supply,
The correction means acquires a high voltage reference voltage having a large value from the pair of reference voltages and a low voltage reference voltage having a small value from the pair of reference voltages from the detection circuit, and obtains the low voltage reference from the high voltage reference voltage. Find the ratio of the value obtained by subtracting the low-voltage reference voltage from the detected voltage to the value obtained by subtracting the voltage,
The liquid level detection system according to claim 1, wherein the calculation unit calculates the liquid level height from the ratio based on the detection voltage obtained by the correction unit. The current control unit sequentially outputs the pair of reference currents,
The detection circuit sequentially generates the pair of reference voltages according to the strength of the pair of reference currents,
The correction means acquires the pair of the high-voltage reference voltage and the low-voltage reference voltage that are sequentially generated by the detection circuit, and subtracts the low-voltage reference voltage from the high-voltage reference voltage to the low-voltage from the detection voltage. The liquid level detection system according to claim 2, wherein a ratio of values obtained by subtracting the reference voltage is obtained. In response to the start of power supply to the liquid level detection system by the power source, the current control unit starts applying the voltage by the sensor power source unit, and then outputs the reference current and outputs the detection current. Output,
The detection circuit generates the detection voltage after generating the reference voltage,
The liquid level detection system according to claim 1, wherein the correction unit corrects the detection voltage with the reference voltage generated before the detection voltage. The current control unit outputs the reference current for each preset period,
The correction means uses the reference voltage generated by the detection circuit according to the intensity of the reference current output for each cycle, and the detection generated by the detection circuit after the reference voltage. The liquid level detection system according to claim 1, wherein the voltage is corrected.

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