DEVICE AND METHOD FOR DETECTING WATER LEVEL OF WATER TRAP IN FUEL CELL

A device and a method for detecting a water level of a water trap in a fuel cell can accurately output a water level of water collected in the water trap by reaction of the fuel cell. The device and the method for detecting a water level of a water trap can detect a change in a surrounding temperature of a water level sensor by mounting a separate temperature sensor in the water level sensor and accurately output the water level in the water trap regardless of the change of the surrounding temperature through a water sensor output value correction algorithm based on a detected temperature.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims under 35 U.S.C. §119(a) the benefit of Korean Patent Application No. 10-2016-0056187 filed on May 9, 2016, the entire contents of which are incorporated herein by reference.

BACKGROUND

(a) Technical Field

The present invention relates to a device and a method for detecting a water level of a water trap, more particularly, to a device and a method for detecting a water level of a water trap in a fuel cell, which can accurately output a water level of water collected in the water trap by reaction of the fuel cell.

(b) Description of the Related Art

A primary energy source of a fuel cell vehicle is caused from a generating device called a fuel cell stack, and the fuel cell stack is a device in which oxygen in air and hydrogen supplied from the outside chemically react to each other to generate energy.

When hydrogen as fuel is supplied to an anode of the fuel cell stack and air as oxidant is supplied to a cathode of the fuel cell stack, the supplied hydrogen is separated into hydrogen ions and electrons by a catalyst layer oxidation reaction in the anode. The generated hydrogen ions are supplied to the cathode through a polymer electrolyte membrane in the fuel cell stack, and the electrons are supplied to the cathode through an external circuit. As a result, in the cathode, electricity is generated through a principle in which the supplied oxygen and the electrons meet to generate oxygen ions by a catalyst layer reduction reaction and the hydrogen ions and the oxygen ions are combined to generate water.

In this case, since the water generated in the fuel cell stack interrupts the flow of the oxygen and the hydrogen, the water needs to be removed from the fuel cell stack. Therefore, the generated water drops down by gravity according to a design structure of the fuel cell stack to be collected in a water trap.

When the water collected in the water trap reaches a predetermined water level or more, an opening control of a drain valve is performed so as to discharge the water to the outside by detecting that the collected water reaches the predetermined water level or more by a water level sensor.

As described above, only by accurately detecting the water level of the water stored in the water trap, the current water level in the water trap can be accurately determined and moreover, a time of discharging the water to the outside can be accurately controlled.

However, the water level sensor mounted on the water trap as a capacitive analog water level sensor shows a water level output within a normal range under a room temperature condition, but shows an output different from an actual water level when the temperature of the water and a surrounding environmental temperature are changed.

For example, the water level sensor has a tendency to output a water level which is higher than the actual water level as the temperature of the water increases.

SUMMARY

The present invention provides a device and a method for detecting a water level of a water trap, which can detect a change in a surrounding temperature of a water level sensor by mounting a separate temperature sensor in the water level sensor and accurately output the water level in the water trap regardless of the change of the surrounding temperature through a water sensor output value correction algorithm based on a detected temperature.

In one aspect, the present invention provides a device for detecting a water level of a water trap, including: a water level sensor mounted on the water trap; a temperature sensor mounted on the water level sensor; and a control unit correcting an output value of the water level sensor depending on a current detection temperature of the temperature sensor to an output value of the water level sensor depending on a reference temperature.

In a preferred embodiment, the temperature sensor may be mounted on the periphery of an electrode of the water level sensor.

In another preferred embodiment, the control unit may store a correction value for correcting an output value of the water level sensor for each current temperature detected by the temperature sensor to the output value of the water level sensor depending on the reference temperature.

In another aspect, the present invention provides a method for detecting a water level of a water trap, including: i) acquiring output data of the water level sensor at a reference temperature; ii) acquiring output value data of the water level sensor for each surrounding temperature; iii) calculating a correction value for the output value of the water level sensor for each surrounding temperature based on an output value of the water level sensor at the reference temperature; and iv) correcting the output value of the water level sensor for each surrounding temperature based on the calculated correction value.

In step i), as the output data of the water level sensor, an output value of the water level sensor for a condition in which a water level in the water trap is a low water level or a full water level at the reference temperature and an output value of the water level sensor in a section between the low water level and the full water level may be acquired.

In step ii), the output value data of the water level sensor for each surrounding temperature may be acquired under the condition in which the water level in the water trap is the low water level.

Step iii) may include iii-1) a process of setting a temperature in the chamber to the temperature lower than the reference temperature and thereafter, increasing the temperature in the chamber to a predetermined temperature higher than the reference temperature at a predetermined temperature step interval, in a state in which the water trap on which the water level sensor including the temperature sensor is mounted is deployed in an environmental chamber, the temperature in the chamber being increased while maintaining each temperature step for a predetermined time; iii-2) a process of recording the output value of the water level sensor and current temperature data at the time when each temperature step ends; and iii-3) a process of subtracting the output value of the water level sensor at the time when each temperature step ends from the output value of the water level sensor at the reference temperature to calculate the correction value for correcting the output value of the water level sensor.

The method may further include: after step iii-3), iii-4) a process of setting the temperature in the chamber to the temperature higher than the reference temperature and thereafter, decreasing the temperature in the chamber to the predetermined temperature lower than the reference temperature at the predetermined temperature step interval, the temperature in the chamber being decreased while maintaining each temperature step for a predetermined time; iii-5) a process of recording the output value of the water level sensor and the current temperature data at the time when each temperature step ends; iii-6) a process of subtracting the output value of the water level sensor at the time when each temperature step ends from the output value of the water level sensor at the reference temperature to calculate the correction value for correcting the output value of the water level sensor; and iii-7) calculating a final correction value by averaging the correction value calculated in step iii-3) and the correction value calculated in step iii-6).

Step iv) may be achieved by finding, when a current temperature detected by the temperature sensor is different from the reference temperature, the correction value corresponding to the current temperature in the memory of the control unit and outputting an output value of the water level sensor, on which the found correction value is reflected.

In another aspect, the present invention provides a non-transitory computer readable medium containing program instructions executed by a processor, the computer readable medium including: program instructions that acquire output data of a water level sensor at a reference temperature; program instructions that acquire output value data of the water level sensor for each surrounding temperature; program instructions that calculate a correction value for the output value of the water level sensor for each surrounding temperature based on an output value of the water level sensor at the reference temperature; and program instructions that correct the output value of the water level sensor for each surrounding temperature based on the calculated correction value.

The present invention provides the following effects through the means for solving problems.

First, a separate temperature sensor is mounted in a water level sensor to detect a change of a current surrounding temperature of the water level sensor and correct and output an output value of the water level sensor for each current detected temperature according to an output value of the water level sensor at a reference temperature, and as a result, the water level sensor can continuously output a water level in a water trap with accuracy regardless of the change of the surrounding temperature.

Second, accuracy of an output value indicating the water level of a capacitive analog water level sensor can be improved and a problem that a water level sensor in the related art shows an output different from an actual water level when the temperature of water and a surrounding environmental temperature are changed can be solved.

DETAILED DESCRIPTION

First, an operating flow of a water trap mounted in a fuel cell system and a water level sensor mounted on the water trap will be described below with reference toFIG. 1(RELATED ART) in order to assist understanding of the present invention.

First, when hydrogen is supplied to an anode of the fuel cell stack, unreacted hydrogen which does not react is discharged to an outlet terminal of the anode, and in this case, water contained in the unreacted hydrogen drops by gravity to be collected in the water trap and hydrogen from which droplets are removed is recirculated to an inlet terminal of the anode.

In this case, a water level of the water collected in a water trap10is detected by a water level sensor12mounted on the water trap10in real time, and the water level sensor12is constituted by a water level detecting electrode12-1and a circuit board (PCB)12-2transmitting a water level detection signal to a control unit.

Therefore, when the control unit determines that the water level in the water trap10is a predetermined level or more based on the water level detection signal transmitted from the water level sensor12, the water in the water trap is discharged to the outside by opening control of a drain valve14positioned at the bottom of the water trap.

The water level sensor12mounted on the water trap10as a capacitive analog water level sensor shows a water level output within a normal range under a room temperature condition, but shows an output different from an actual water level when the temperature of the water and a surrounding environmental temperature are changed.

For example, the water level sensor12has a tendency to output a water level which is higher than the actual water level as the temperature of the water increases.

In order to solve the problem, the present invention places emphasis on detecting a change in a surrounding temperature of a water level sensor by mounting a separate temperature sensor in the water level sensor and accurately outputting the water level in the water trap regardless of the change of the surrounding temperature through a temperature correction algorithm based on a detected temperature.

The water level sensor for the water trap and an operating flow thereof according to the present invention will be described below.

Referring toFIG. 2, a separate temperature sensor20is mounted in the water level sensor12mounted in the water trap10.

The water level sensor12is adopted as the capacitive analog water level sensor constituted by the water level detecting electrode12-1and the circuit board (PCB)12-2transmitting the water level detection signal to the control unit and the temperature sensor20is mounted on an adjacent portion of the electrode12-1of the water level sensor12.

The reason for mounting the temperature sensor20on the adjacent portion of the electrode12-1of the water level sensor12is that an output value of the water level sensor12is influenced by a temperature of the electrode12-1.

Therefore, the output value of the water level sensor12influenced by the temperature is corrected by using a detection value of the temperature sensor20, and as a result, the output value of the water level sensor12may be output to a level to accurately indicate the water level in the water trap regardless of a change of a surrounding temperature. A procedure of correcting the output value of the water level sensor in accordance with the surrounding temperature according to the present invention will be described below.

First, output data of the water level sensor for a condition in which the water level in the water trap is a low water level (empty) and a full water level (full) at a reference temperature Ta is acquired.

Output values C1and C2of the water level sensor for the condition in which the water level in the water trap is the low water level (empty) and the full water level (full) at the reference temperature Ta and an output value (C=f(x)) of the water level sensor in a section between the low water level (empty) and the full water level (full) are output substantially linearly as illustrated inFIG. 3.

Therefore, the output values C1and C2of the water level sensor for the condition in which the water level in the water trap is the low water level (empty) and the full water level (full) at the reference temperature Ta and the output value (C=f(x)) of the water level sensor in the section between the low water level (empty) and the full water level (full) are stored in a memory of the control unit.

Next, output value data of the water level sensor for each surrounding temperature under the condition in which the water level in the water trap is the low water level is acquired.

In this case, the reason for acquiring the output value of the water level sensor for each surrounding temperature only under the condition of the low water level is that the output values of the water level sensor for each surrounding temperature under the condition in which the water level in the water trap is the low water level, the condition between the low water level and the full water level, and the condition of the full water level are similarly changed.

Referring toFIG. 4, in the case of the change of the output value of the water level sensor for each surrounding temperature under the low water level (empty) condition, the output value at a temperature T_LOW lower than the reference temperature Ta is output to be lower than an output value C3at the reference temperature Ta and the output value at a temperature T_HIGH higher than the reference temperature Ta is output to be higher than the output value C3. Therefore, this shows that the output value of the water level sensor is changed according to the surrounding temperature.

Subsequently, a correction value K for the output value of the water level sensor for each surrounding temperature (for example, for each surrounding temperature of the electrode) is calculated based on the output value of the water level sensor at the reference temperature Ta.

An example of a method for calculating the correction value K will be described below with reference to a flowchart ofFIG. 7.

The water trap on which the water level sensor including the temperature sensor is mounted is deployed in an environmental chamber (S101).

Next, a temperature in the chamber is set to the temperature T_LOW lower than the reference temperature Ta and thereafter, increased to a predetermined temperature T_HIGH higher than the reference temperature Ta at a temperature step interval of 2° C. and a minimum of 180 seconds are maintained per each temperature step (S102).

In this case, the output value of the water level sensor and current temperature data are recorded at the time when each temperature step ends (S103).

Subsequently, the output value of the water level sensor at the time when each temperature step ends is subtracted from the output value of the water level sensor at the reference temperature to calculate the correction value K for correcting the output value of the water level sensor (S104).

Meanwhile, the temperature in the chamber is set to the temperature T_HIGH higher than the reference temperature Ta, and thereafter, the correction value is calculated once again, in order to increase the accuracy of the calculation of the correction value K.

To this end, the temperature in the chamber is set to the temperature T_HIGH higher than the reference temperature Ta and thereafter, decreased to a predetermined temperature T_LOW lower than the reference temperature Ta at the temperature step interval of 2° C. and a minimum of 180 seconds are maintained per each temperature step (S105).

Even in this case, the output value of the water level sensor and current temperature data are recorded at the time when each temperature step ends (S106).

Similarly, the output value of the water level sensor at the time when each temperature step ends is subtracted from the output value of the water level sensor at the reference temperature to calculate the correction value K for correcting the output value of the water level sensor (S107).

As described above, the step of calculating the correction value is repeated twice, and resulting values repeated twice are averaged to calculate a final correction value K (S108).

The finally calculated correction value K is made to a table or an equation to be stored in the memory of the control unit.

Accordingly, the output value of the water level sensor may be corrected for each surrounding temperature based on the calculated correction value.

In particular, when a current temperature Tb detected by the temperature sensor is different from the reference temperature Ta as illustrated inFIG. 5, the correction value K corresponding to the current temperature Tb is found in the memory of the control unit, and an output value of the water level sensor on which the found correction value K is reflected is output.

For example, assuming that the reference temperature Ta is 10° C. and the output value of the water level sensor at the reference temperature Ta of 10° C. is 100, and assuming that the current temperature Tb detected by the temperature sensor is −10° C. and that the output value of the water level sensor at the current temperature Tb of −10° C. is 50, the correction value becomes 50, and consequently, the output value of the water level sensor, on which the correction value of 50 is reflected becomes 100.

As described above, the separate temperature sensor is mounted in the water level sensor to detect the change of the current surrounding temperature of the water level sensor and correct and output the output value of the water level sensor for each current detected temperature according to the output value of the water level sensor at the reference temperature, and as a result, the water level sensor can continuously output the water level in the water trap with accuracy regardless of the change of the surrounding temperature.

In other words, the output value of the water level sensor for each surrounding temperature for a specific water level varies as compared with the output value at the reference temperature Ta as illustrated inFIG. 6in the related art, but according to the present invention, a constant output value of the water level sensor at the specific water level may be output as compared with the output value at the reference temperature Ta regardless of the surrounding temperature, and consequently, the accuracy of the output value indicating the water level of the capacitive analog water level sensor may be improved.