JP2023089668A - Control device for gas sensors - Google Patents

Abstract

To provide a control device for gas sensors with which it is possible to reduce power consumption when detecting a gas concentration.SOLUTION: A control device 100 for a gas sensor 4 comprises a current detection unit 110 for detecting the current flowing in a heater RH, and a current supply unit 120 for controlling the current supplied to the heater RH on the basis of the current detected by the current detection unit 110. Preferably, the current supply unit 120 includes a switch element 123, and a control circuit 120 for controlling the conduction and non-conduction of electricity to the switch element 123 on the basis of a current IH detected by the current detection unit 110. More preferably, the control device 100 controls the conduction time and non-conduction time of electricity to the switch element 123 so that the current flowing in the heater RH falls within a certain range IREFa to IREFb when electricity is conducted to the switch element 123 and the heater RH is supplied with a current.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to a gas sensor control device.

In recent years, hydrogen has attracted attention as a fuel that does not emit greenhouse gases such as carbon dioxide. In fuel cell vehicles, hydrogen vehicles, etc., which use hydrogen as an energy source, it is necessary to check for hydrogen leakage. Gas sensors are used for this purpose.

For example, Japanese Unexamined Patent Application Publication No. 2015-127642 discloses a gas sensor provided with a metal oxide semiconductor film for gas detection and a heater.

JP 2015-127642 A

Conventionally, a heater is used to bring the gas sensor to a temperature suitable for gas detection. However, in recent years, demand for power saving has been increasing for devices for vehicles, and it is necessary to prevent power loss due to overheating of the heater temperature.

An object of the gas sensor control device of the present disclosure is to reduce power consumption when detecting gas concentration using a gas sensor.

The present disclosure relates to a control device that controls a gas sensor that incorporates a sensing element and a heater that heats the sensing element. A control device for the gas sensor includes a current detection section that detects current flowing through the heater, and a current supply section that controls the current supplied to the heater based on the current detected by the current detection section.

According to the gas sensor control device according to the present disclosure, the power consumption of the gas sensor can be reduced by suppressing the power of the heater.

1 is a block diagram showing the configuration of a gas sensor and a control device for the gas sensor according to the first embodiment; FIG. 4 is a diagram showing configurations of a current detection unit and a current supply unit according to the first embodiment; FIG. 4 is a waveform diagram showing an example of control waveforms in Embodiment 1. FIG. It is a figure which shows the characteristic of the resistance change by the temperature of the wire of a heater. It is a figure which shows the relationship between temperature and the electric current which flows into a heater. 2 is a diagram showing a configuration example of a density detection circuit 130 shown in FIG. 1; FIG. FIG. 10 is a diagram showing the configuration of a current detection section 110A and a current supply section 120A according to Embodiment 2; 8 is a waveform diagram showing an example of control waveforms in Embodiment 2. FIG. 4 is a flowchart for explaining control executed by a current detection unit 110A;

Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a block diagram showing the configuration of a gas sensor and a control device for the gas sensor according to the first embodiment. FIG. 1 shows a gas sensor 4 and a control device 100 that controls the gas sensor 4 .

Gas sensor 4 includes sensor unit 2 and resistor RL. The sensor unit 2 includes a heater RH and a sensing element RS. When a voltage VRH is applied to the heater RH from the outside, the heater RH heats the sensing element RS.

Although the sensing element RS is not particularly limited, it can be an oxide semiconductor sensor, for example. In the semiconductor type gas sensor, the resistance value changes according to the change in the oxygen concentration on the surface of the element.

When the sensing element is heated to several hundred degrees and placed in the air, a reaction occurs between a reducing gas such as hydrogen and oxygen adsorbed on the surface of the sensing element, reducing the oxygen concentration and reducing the resistance value. When the reducing gas is removed, the oxygen concentration increases to its pre-existing concentration and the resistance returns to its pre-exposure value.

The resistance value of the sensing element RS is obtained by the following equation (1).
RS=(VC/VOUT-1)×RL (1)
In equation (1), RS indicates the resistance value of the sensing element RS, RL indicates the resistance value of the resistor RL, VC indicates the difference between the terminal voltages VC(+) and VC(-), and VOUT indicates the terminal voltage VOUT. It shows the difference between (+) and VOUT(-). VC=5.0 V is supplied to the gas sensor 4, for example.

By measuring the resistance value R0 of the sensor in clean air in advance, the gas concentration can be obtained based on the rate of change in resistance (RS/R0). The concentration detection circuit 130 calculates the resistance value (RS) of the detection element and calculates the resistance change rate (RS/R0). By storing the relationship between the concentration of the gas to be detected and the resistance change rate in a map in advance, the concentration detection circuit 130 can detect the gas concentration based on the terminal voltages VC(+) and VOUT(+) of the detection element RS. can output a signal COUT that indicates

The gas to be detected is typically hydrogen, but may be carbon monoxide, ethanol, methane, isobutane, or the like.

FIG. 2 is a diagram showing configurations of a current detection unit and a current supply unit according to the first embodiment. Current detector 110 includes comparators 111 and 112 and edge detector 113 .

Current supply unit 120 includes a switch element 123 and a control circuit 125 that controls conduction and non-conduction of switch element 123 based on current IH detected by current detection unit 110 . Switch element 123 is connected in series with load resistance element RD and heater RH. Switch element 123 can be, for example, a P-channel MOSFET. The control circuit 125 includes a timer 121, a pre-driver 122, and a comparator 124, for example.

FIG. 3 is a waveform diagram showing an example of control waveforms according to the first embodiment. As shown in FIG. 3, the current supply unit 120 supplies current to the heater RH so that the temperature of the heater RH becomes around 300° C. to 400° C. by repeating ON and OFF of the FET, which is the switch element 123 . to control.

FIG. 4 is a diagram showing characteristics of resistance change depending on the temperature of the wire rod of the heater. FIG. 5 is a diagram showing the relationship between the temperature and the current flowing through the heater. As shown in FIG. 4, the wire of the heater RH has a characteristic that the resistance value increases as the temperature rises. Therefore, when the voltage VH in FIG. 2 is constant, the current value flowing through the heater RH decreases as the temperature increases, as shown in FIG. Therefore, the temperature of the heater RH can be detected by detecting the current flowing through the heater RH.

During the ON period of the FET, which is the switch element 123, a voltage drop V(IH) occurs across the load resistance element RD in proportion to the current IH flowing through the heater.

As shown in FIG. 5, the current value corresponding to a temperature of 400° C. is IREFa, and the current value corresponding to a temperature of 300° C. is IREFb. It is also assumed that the voltage is V(IREFa) when the current value IREFa flows through the load resistance element RD, and the voltage is V(IREFb) when the current value IREFb flows through the load resistance element RD.

When the FET, which is the switch element 123, is ON, the temperature of the heater rises from 300.degree. C. to 400.degree. During this time, comparators 111 and 112 compare the voltage of load resistance element RD with threshold values V(IREFa) and V(IREFb).

The edge detection unit 113 detects edges from changes in the outputs of the comparators 111 and 112, thereby outputting low-active signals C1 and C2. The timer 121 determines the ON period of the FET, which is the switch element 123, by counting the time from when the signal C2 changes to when the signal C1 changes. When the signal C1 is output, the switch element 123 is turned off, and after counting the initially set time, the switch element 123 is turned on again to observe the signals C1 and C2. At this time, if the signal C2 can be observed at the beginning of the ON period of the FET, the OFF period is appropriate. Also, if the signal C2 cannot be observed during the ON period of the FET, the OFF period is too short and the temperature is biased toward 400.degree. Also, if it takes too much time from the start of the ON period of the FET to the observation of the signal C2, the OFF period is too long and the temperature falls below 300° C. in too many periods.

Therefore, the timer 121 increases or decreases the ON period and OFF period while observing the signals C1 and C2, and as shown in FIG. set.

When gas is not detected, the power consumption of the heater can be reduced by detecting the gas concentration during the ON period of the FET as shown in FIG.

Further, when gas is detected, the comparator 124 in FIG. 2 forcibly drives the pre-driver 122 to change the switch element 123 to the constantly ON state. Therefore, it is possible to continuously monitor the gas concentration.

In this way, when the possibility of gas leakage is high, the gas concentration can be observed in detail by increasing the gas detection frequency.

FIG. 6 is a diagram showing a configuration example of the density detection circuit 130 shown in FIG. Density sensing circuit 130 includes a central processing unit (CPU) 131 , a memory 132 and an A/D converter 133 .

A/D converter 133 receives terminal voltages VC(+), VC(−), VOUT(+), and VOUT(−), performs A/D conversion, and outputs corresponding digital values to CPU 131 . The CPU 131 calculates VC, which is the difference between the terminal voltages VC(+) and VC(-), and VOUT, which is the difference between the terminal voltages VOUT(+) and VOUT(-). Substitute to find the resistance value of the sensing element RS.

The CPU 131 further divides the resistance value of the sensing element RS by the resistance value R0 of the sensor in clean air to obtain a resistance change rate (RS/R0).

The memory 132 stores, as a map, the correspondence between the rate of change in resistance and the concentration of the gas to be detected, which is experimentally obtained in advance. The CPU 131 refers to the map stored in the memory 132 to obtain the gas concentration corresponding to the calculated rate of change in resistance, and outputs a signal COUT indicating the gas concentration.

As described above, the concentration detection circuit 130 can output the signal COUT indicating the gas concentration based on the terminal voltages VC(+) and VOUT(+) of the detection element RS.

By interlocking the concentration detection circuit 130 and the current supply unit 120, the concentration detection circuit 130 updates the signal COUT during the FET ON period, and the concentration detection circuit 130 updates the FET ON period during the FET OFF period. It is preferable to keep the signal COUT updated at the end of .

[Embodiment 2]
Since the temperature cannot be measured unless current is flowing through the heater, in the first embodiment, a timer is used to set the ON/OFF period of the switch element 123 . However, by periodically providing an extremely short ON period in the OFF period of the switch element 123, the temperature of the heater can be lowered while monitoring the temperature. In this way, the ON period can be ended when the heater temperature reaches 400° C., and the OFF period can be ended when the heater temperature becomes lower than 300° C. without using a timer.

The gas sensor control apparatus of the second embodiment includes a current detection section 110A instead of the current detection section 110 and a current supply section 120A instead of the current supply section 120 in the configuration of the control apparatus 100 of FIG. Density detection circuit 130 has the same configuration as that shown in FIG. 6, and therefore description thereof will not be repeated.

FIG. 7 is a diagram showing the configuration of a current detection section 110A and a current supply section 120A according to the second embodiment. The current detector 110A includes an A/D converter 111A. 120 A of electric current supply parts are equipped with 125 A of control circuits, and the switch element 123. FIG. The control circuit 125A includes a CPU 121A, a memory 126A, a pre-driver 122, and a comparator 124.

The A/D converter 111A A/D-converts the voltage across the load resistance element RD and outputs it to the CPU 121A. The CPU 121A receives the output of the A/D converter 111A, divides the voltage applied to the load resistance element RD by the resistance value, calculates the current flowing through the heater RH, and calculates the resistance change stored in the memory 126A. The temperature of the heater RH is detected from a map showing the relationship between rate and temperature. The CPU 121A outputs a drive signal to the pre-driver 122 based on the detected temperature of the heater RH.

FIG. 8 is a waveform diagram showing an example of control waveforms according to the second embodiment. FIG. 9 is a flowchart for explaining the control executed by the current detector 110A.

110 A of electric current detection parts set the switch element 123 to ON in step S1 first, and measure the temperature of the heater RH from the electric current which flows. Then, in step S2, the current detector 110A determines whether or not the temperature T of the heater RH is higher than the threshold TH (eg, 400° C.). When the temperature T is equal to or lower than the threshold TH (NO in S2), the current detector 110A executes the process of step S1 again. Thus, until the temperature T of the heater RH exceeds the threshold TH, the switch element 123 is kept ON as shown in FIG.

When the temperature T of the heater RH becomes higher than the threshold TH (YES in S2), in step S3, the current detector 110A turns off the switch element 123 and waits for a certain period of time. This lowers the temperature of the heater RH. Then, in step S4, the current detection unit 110A sets the switch element 123 to ON, and measures the temperature of the heater RH from the flowing current. Subsequently, in step S5, the current detector 110A determines whether or not the temperature T of the heater RH is lower than the threshold TL (eg, 300° C.). When temperature T is equal to or higher than threshold TL (NO in S5), current detection unit 110A executes steps S3 and S4 again. In this manner, the temperature T of the heater RH gradually decreases from TH to TL as shown in the OFF period of FIG. In the meantime, the switch element 123 is periodically turned ON for a short time to monitor the temperature change of the heater RH.

When the temperature T of the heater RH becomes lower than the threshold value TL (YES in S5), the current detection unit 110A repeats the processes from step S1 onwards.

The gas sensor control device shown in the second embodiment can also reduce the power consumption of the heater RH as in the first embodiment.

In the second embodiment, the CPU shown in FIG. 6 and the CPU 121A shown in FIG. 7 may be realized by one CPU. In this case, the memory and A/D converter may also be shared.

The above embodiments will be summarized with reference to the drawings again. As shown in FIG. 1, the present disclosure relates to a control device 100 that controls a gas sensor 4 that incorporates a sensing element RS and a heater RH that heats the sensing element RS. The control device 100 of the gas sensor 4 includes a current detection section 110 that detects the current flowing through the heater RH, and a current supply section 120 that determines the time during which the current is supplied to the heater RH and the time during which the current is not supplied to the heater RH. .

Preferably, as shown in FIGS. 2 and 7, the current supply unit 120 controls the conduction and non-conduction of the switch element 123 based on the switch element 123 and the current IH detected by the current detection unit 110. and circuits 125 and 125A.

More preferably, as shown in FIGS. 2 to 5, the control device 100 allows the current flowing through the heater RH to fall within a certain range IREFa to IREFb when the switch element 123 is turned on and current is supplied to the heater RH. , the conduction time and non-conduction time of the switch element 123 are controlled.

More preferably, as shown in FIG. 7, current detection section 110A includes a voltage detection section (A/D converter 111A) that measures the voltage of load resistance element RD connected in series with heater RH and switch element 123. .

More preferably, the control circuits 125 and 125A increase the time during which no current is supplied to the heater RH when the gas sensor detects gas compared to when the gas sensor does not detect gas, and the current is supplied to the heater RH. reduce the time to feed That is, when the comparator 124 detects gas, the switch element 123 is turned on to supply current to the heater RH, thereby realizing such control.

Preferably, as shown in FIG. 1, the gas sensor control device 100 further includes a concentration detection circuit 130 that outputs a signal COUT indicating the gas concentration based on the terminal voltages VC(+) and VOUT(+) of the detection element RS. Prepare.

The embodiments disclosed this time should be considered as examples and not restrictive in all respects. The scope of the present invention is indicated by the scope of the claims rather than the description of the above-described embodiments, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

2 sensor unit, 4 gas sensor, 100 control device, 110, 110A current detector, 111, 112, 124 comparator, 121A, 131 CPU, 126A, 132 memory, 113 edge detector, 111A, 133 A/D converter, 120, 120A current supply unit, 121 timer, 122 pre-driver, 123 switch element, 130 concentration detection circuit, RD load resistance element, RH heater, RL resistor, RS detection element.

Claims (6)

A control device for controlling a gas sensor containing a detection element and a heater for heating the detection element,
a current detection unit that detects a current flowing through the heater;
A control device for a gas sensor, comprising: a current supply unit that determines a time during which current is supplied to the heater and a time during which current is not supplied to the heater, based on the current detected by the current detection unit. The current supply unit
a switch element;
2. The gas sensor control device according to claim 1, further comprising a control circuit for controlling conduction and non-conduction of said switch element based on the current detected by said current detection section. The control circuit controls the conduction time and the non-conduction time of the switch element so that the current flowing through the heater falls within a certain range when the switch element is turned on and current is supplied to the heater. The gas sensor control device according to claim 2 . When the gas sensor detects gas, the control circuit increases the time during which current is not supplied to the heater compared to when the gas sensor does not detect gas, and increases the time during which current is supplied to the heater. 4. The gas sensor control device according to claim 2 or 3, which reduces . The current detection unit is
5. The gas sensor control device according to claim 2, further comprising a voltage detection section for measuring a voltage of a load resistance element connected in series with said heater and said switch element. 5. The gas sensor control device according to claim 1, further comprising a concentration detection circuit that outputs a signal indicating gas concentration based on the terminal voltage of said detection element.

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