JP7586104B2 - Concentration Detector - Google Patents

Description

This disclosure relates to a concentration detection device that detects gas concentration.

Patent document 1 describes a method of applying an applied voltage, which is an AC voltage superimposed on a DC voltage, to a gas sensor, detecting the gas concentration based on a signal obtained by removing high-frequency components from the concentration detection signal output from the gas sensor, and detecting the element resistance value of the gas sensor based on a signal obtained by removing low-frequency components from the concentration detection signal.

U.S. Pat. No. 4,419,190

In recent years, as exhaust gas regulations have become stricter, there has been an increasing demand for smaller exhaust gas sensors to improve their mountability, as well as for improved gas concentration detection accuracy of exhaust gas sensors.

To detect the concentration of a specific gas (e.g., oxygen) contained in exhaust gas, it is necessary to maintain the sensor element of the gas sensor at a specified temperature. For this reason, a heater is built into the gas sensor and the amount of electricity passed through the heater is controlled. Because electricity is passed through the heater using duty ratio control, electrical noise is generated when electricity to the heater is switched on and off, degrading the accuracy of gas concentration detection. Additionally, noise such as electromagnetic waves generated by the vehicle environment also degrades the accuracy of gas concentration detection.

The purpose of this disclosure is to suppress deterioration in gas concentration detection accuracy caused by noise.

One aspect of the present disclosure is a concentration detection device (30, 7) including a high-frequency extraction unit (31, S30), a delay unit (32, S20), and a subtraction unit (33, S40).
The high frequency extraction unit is configured to acquire from the gas sensor (2) a concentration detection signal whose value changes according to the concentration of the specific gas, and to generate a high frequency extraction signal by extracting high frequency components from the acquired concentration detection signal. The gas sensor detects the concentration of the specific gas contained in the measurement target gas.

The delay unit is configured to acquire a concentration detection signal from the gas sensor and generate a delayed signal by delaying the acquired concentration detection signal by the high-frequency extraction processing time required for the high-frequency extraction unit to generate the high-frequency extraction signal.

The subtraction unit is configured to subtract the high-frequency extracted signal generated by the high-frequency extraction unit from the delayed signal generated by the delay unit.
The concentration detection device of the present disclosure configured in this manner can reduce noise superimposed on the concentration detection signal, and can suppress deterioration in gas concentration detection accuracy.

FIG. 2 is a diagram showing a configuration of a gas sensor control device according to the first and second embodiments. FIG. 2 is a diagram showing a configuration of a concentration current detection circuit according to the first embodiment. 4 is a timing chart showing a noise removal method according to the first embodiment. FIG. 13 is a diagram showing a configuration of a concentration current detection circuit according to a second embodiment. 10 is a timing chart showing a noise removal method according to a second embodiment. FIG. 13 is a diagram showing a configuration of a gas sensor control device according to third and fourth embodiments. 13 is a flowchart showing a concentration current detection process according to a third embodiment. 13 is a flowchart showing a concentration current detection process according to the fourth embodiment.

[First embodiment]
A first embodiment of the present disclosure will be described below with reference to the drawings.
A gas sensor control device 1 of this embodiment is mounted on a vehicle and controls a gas sensor 2 as shown in FIG.

The gas sensor 2 includes a sensor element 3 and a heater 4 .
The sensor element 3 is attached to an exhaust pipe of a vehicle and detects the concentration of oxygen contained in exhaust gas discharged from the engine of the vehicle into the exhaust pipe. The sensor element 3 has a first terminal 3a and a second terminal 3b. When a predetermined constant voltage is applied between the first terminal 3a and the second terminal 3b, the sensor element 3 outputs a concentration detection current having a current value corresponding to the oxygen concentration of the exhaust gas from the second terminal 3b.

The heater 4 heats the sensor element 3 so that it can detect the oxygen concentration in the exhaust gas.
The gas sensor control device 1 includes a sensor control unit 5 , a heater control unit 6 , a microcomputer 7 (hereinafter, referred to as MCU 7 ), a first sensor terminal 8 , a second sensor terminal 9 , and a heater terminal 10 .

The sensor control unit 5 includes a sensor control circuit 11 , D/A converters 12 and 13 , operational amplifiers 14 and 15 , a shunt resistor 16 , and an A/D converter 17 .
The sensor control circuit 11 is realized by an application specific integrated circuit (ASIC). The ASIC is an abbreviation for Application Specific IC. The sensor control circuit 11 includes a concentration current detection circuit 30.

The D/A converter 12 generates an analog signal having a voltage value corresponding to the digital value input from the sensor control circuit 11 , and outputs the analog signal to the non-inverting input terminal of the operational amplifier 14 .
The D/A converter 13 generates an analog signal having a voltage value corresponding to the digital value input from the sensor control circuit 11 , and outputs the analog signal to the non-inverting input terminal of the operational amplifier 15 .

The output terminal of the operational amplifier 14 is connected to the inverting input terminal of the operational amplifier 14 and is also connected to the first sensor terminal 8. The first sensor terminal 8 is connected to the first terminal 3a of the sensor element 3. This causes the operational amplifier 14 to function as a buffer that outputs the first voltage indicated by the sensor control circuit 11 to the first terminal 3a of the sensor element 3.

The output terminal of the operational amplifier 15 is connected to the inverting input terminal of the operational amplifier 15 and is also connected to the second sensor terminal 9 via the shunt resistor 16. The second sensor terminal 9 is connected to the second terminal 3b of the sensor element 3. This causes the operational amplifier 15 to function as a buffer that outputs the second voltage indicated by the sensor control circuit 11 to the second terminal 3b of the sensor element 3.

The A/D converter 17 converts the voltage across the shunt resistor 16 into a digital value and outputs it to the concentration current detection circuit 30 .
The sensor control circuit 11 changes the digital value output to the D/A converters 12 and 13 so that the AC voltage whose voltage value oscillates at a predetermined measurement period Tr is superimposed on the above-mentioned predetermined constant voltage.

The heater control unit 6 outputs a PWM signal with a duty ratio required to maintain the sensor element 3 at a predetermined temperature to the heater 4 via the heater terminal 10 based on the sensor element temperature data input from the microcomputer 7. PWM stands for Pulse Width Modulation.

The microcomputer 7 includes a CPU 21, a ROM 22, and a RAM 23. The various functions of the microcomputer 7 are realized by the CPU 21 executing a program stored in a non-transitive physical recording medium. In this example, the ROM 22 corresponds to the non-transitive physical recording medium storing the program. Furthermore, the execution of this program executes a method corresponding to the program. Note that some or all of the functions executed by the CPU 21 may be configured in hardware using one or more ICs, etc.

As shown in FIG. 2, the concentration current detection circuit 30 includes a digital high-pass filter 31, a delay circuit 32, a subtractor 33, a current value calculation circuit 34, and an element resistance calculation circuit 35.
The digital high-pass filter 31 outputs a digital signal obtained by removing low-frequency components from the digital signal input from the A/D converter 17 .

The delay circuit 32 delays the digital signal input from the A/D converter 17 by a preset delay time and outputs the delayed signal.
The subtractor 33 outputs a digital signal corresponding to a value obtained by subtracting the digital value of the digital signal input from the digital high-pass filter 31 from the digital value of the digital signal input from the delay circuit 32 .

The current value calculation circuit 34 calculates the current value of the concentration detection current output from the sensor element 3 based on the digital signal output from the subtractor 33, and outputs a digital signal indicating this voltage value to the microcomputer 7. The microcomputer 7 calculates the oxygen concentration based on the digital signal input from the current value calculation circuit 34.

The element resistance calculation circuit 35 calculates the element resistance value of the sensor element 3 based on the digital signal output from the digital high-pass filter 31, and outputs a digital signal indicating this element resistance value to the microcomputer 7. The microcomputer 7 calculates the temperature of the sensor element 3 based on the digital signal input from the element resistance calculation circuit 35.

FIG. 3 is a timing chart showing the change over time of the digital signals output from the A/D converter 17, the digital high-pass filter 31, the delay circuit 32 and the subtractor 33. As shown in FIG.
As shown in FIG. 3, the digital signal DS1 output from the A/D converter 17 includes a concentration detection current component C1, an element resistance current component C2, a heater noise component C3, and a vehicle environment noise component C4.

The concentration detection current component C1 is the current value of the concentration detection current. The element resistance current component C2 is the current value of the element resistance current generated due to the AC voltage that oscillates during the measurement period Tr. The element resistance current component C2 repeatedly increases and decreases during the measurement period Tr.

The heater noise component C3 is the current value of noise generated due to the on/off switching of the PWM signal input to the heater 4. The vehicle environment noise component C4 is the current value of noise generated due to electromagnetic waves inside the vehicle.

The digital signal DS2 output from the digital high-pass filter 31 is a signal obtained by removing low-frequency components from the digital signal DS1. In the first embodiment, the frequency of the element resistance current component C2 is included in the frequency range that the digital high-pass filter 31 can extract. Therefore, the digital signal DS2 includes the element resistance current component C2, the heater noise component C3, and the vehicle environment noise component C4. The digital signal DS2 is output with a delay of the delay time Td1 from the input of the digital signal DS1 due to the processing in the digital high-pass filter 31.

The digital signal DS3 output from the delay circuit 32 is a signal obtained by delaying the digital signal DS1 by the delay time Td1. Therefore, the digital signal DS3 includes a concentration detection current component C1, an element resistance current component C2, a heater noise component C3, and a vehicle environment noise component C4.

The digital signal DS4 output from the subtractor 33 is a signal obtained by subtracting the digital signal DS2 from the digital signal DS3. Therefore, the digital signal DS4 contains only the concentration detection current component C1. The digital signal DS4 is output with a delay of the delay time Td2 from the input of the digital signal DS3 due to the processing in the subtractor 33.

The concentration current detection circuit 30 of the gas sensor control device 1 configured as above includes a digital high-pass filter 31 , a delay circuit 32 , and a subtractor 33 .
The digital high-pass filter 31 is configured to receive from the gas sensor 2 a concentration detection signal whose value changes according to the concentration of oxygen (i.e., the digital signal DS1 output from the A/D converter 17) and generate a high-frequency extraction signal by extracting high-frequency components from the received concentration detection signal. The gas sensor 2 detects the concentration of oxygen contained in the exhaust gas.

The delay circuit 32 is configured to acquire a concentration detection signal from the gas sensor 2 and generate a delayed signal by delaying the acquired concentration detection signal by the delay time Td1 required for the digital high-pass filter 31 to generate a high-frequency extraction signal.

The subtractor 33 is configured to subtract the high frequency extraction signal generated by the digital high pass filter 31 from the delayed signal generated by the delay circuit 32 .
Such a concentration current detection circuit 30 can reduce noise superimposed on the concentration detection signal, and can suppress deterioration in gas concentration detection accuracy.

The concentration current detection circuit 30 also includes an element resistance calculation circuit 35 configured to calculate the element resistance value of the sensor element 3 included in the gas sensor 2 based on the high-frequency extraction signal generated by the digital high-pass filter 31. This allows the concentration current detection circuit 30 to detect the element resistance value of the sensor element 3.

In the embodiment described above, the concentration current detection circuit 30 corresponds to the concentration detection device, the digital high-pass filter 31 corresponds to the high-frequency extraction section, the delay circuit 32 corresponds to the delay section, and the subtractor 33 corresponds to the subtraction section.

Further, the exhaust gas corresponds to the measured gas, oxygen corresponds to the specific gas, the digital signal DS1 corresponds to the concentration detection signal, the delay time Td1 corresponds to the high frequency extraction processing time, and the element resistance calculation circuit 35 corresponds to the element resistance calculation section.
[Second embodiment]
A second embodiment of the present disclosure will be described below with reference to the drawings. In the second embodiment, differences from the first embodiment will be described. The same reference numerals will be used to designate the same components.

The gas sensor control apparatus 1 of the second embodiment differs from that of the first embodiment in that the configuration of the concentration current detection circuit 30 is changed.
As shown in FIG. 4, the concentration current detection circuit 30 of the second embodiment differs from the first embodiment in that the element resistance calculation circuit 35 is omitted and a digital low-pass filter 36 is added.

The digital low-pass filter 36 removes high frequency components from the digital signal input from the subtractor 33 and outputs the resulting digital signal to the current value calculation circuit 34 .
FIG. 5 is a timing chart showing the change over time of the digital signals output from the A/D converter 17, the digital high-pass filter 31, the delay circuit 32, the subtractor 33 and the digital low-pass filter .

As shown in FIG. 5, the digital signal DS11 output from the A/D converter 17 includes a concentration detection current component C1, an element resistance current component C2, a heater noise component C3, and a vehicle environment noise component C4.

The digital signal DS12 output from the digital high-pass filter 31 is a signal obtained by removing low-frequency components from the digital signal DS11. In the second embodiment, the frequency of the element resistance current component C2 is not included in the frequency range that the digital high-pass filter 31 can extract. Therefore, the digital signal DS12 includes a heater noise component C3 and a vehicle environment noise component C4. The digital signal DS12 is output with a delay of a delay time Td1 from the input of the digital signal DS11 due to processing in the digital high-pass filter 31.

The digital signal DS13 output from the delay circuit 32 is a signal obtained by delaying the digital signal DS11 by the delay time Td1. Therefore, the digital signal DS13 includes a concentration detection current component C1, an element resistance current component C2, a heater noise component C3, and a vehicle environment noise component C4.

The digital signal DS14 output from the subtractor 33 is a signal obtained by subtracting the digital signal DS12 from the digital signal DS13. Therefore, the digital signal DS14 includes a concentration detection current component C1 and an element resistance current component C2. The digital signal DS14 is output with a delay of the delay time Td2 from the input of the digital signal DS13 due to the processing in the subtractor 33.

The digital signal DS15 output from the digital low-pass filter 36 is a signal obtained by removing high-frequency components from the digital signal DS14. Therefore, the digital signal DS14 contains only the concentration detection current component C1. The digital signal DS15 is output with a delay of a delay time Td3 from the input of the digital signal DS14 due to the processing in the digital low-pass filter 36.

The concentration current detection circuit 30 of the gas sensor control device 1 configured in this manner further includes a digital low-pass filter 36 in addition to the digital high-pass filter 31, delay circuit 32, and subtractor 33. The digital low-pass filter 36 is configured to extract low-frequency components from the subtraction signal generated by the subtractor 33 by subtracting the high-frequency extraction signal from the delay signal.

Such a concentration current detection circuit 30 can reduce noise superimposed on the concentration detection signal when the frequency of the element resistance current component C2 is not included in the frequency range that the digital high-pass filter 31 can extract, thereby preventing a decrease in the accuracy of gas concentration detection.

In the embodiment described above, the digital low-pass filter 36 corresponds to the low-frequency extraction section, and the digital signal DS11 corresponds to the concentration detection signal.
[Third embodiment]
A third embodiment of the present disclosure will be described below with reference to the drawings. In the third embodiment, differences from the first embodiment will be described. The same reference numerals will be used to designate the same components.

As shown in FIG. 6, the gas sensor control device 1 of the third embodiment differs from the first embodiment in that the concentration current detection circuit 30 is omitted, the A/D converter 17 outputs a digital signal to the microcomputer 7, and the microcomputer 7 executes the concentration current detection process.

Next, the procedure for the concentration current detection process executed by the microcomputer 7 will be described. The concentration current detection process is executed every time a preset signal acquisition period elapses while the microcomputer 7 is in operation.

When the concentration current detection process is executed, the CPU 21 of the microcontroller 7 first acquires the digital signals input from the A/D converter 17 for the most recent signal acquisition cycle in S10, as shown in FIG. 7.

Then, in S20, the CPU 21 delays the digital signal for the signal acquisition cycle acquired in S10 by a delay time Td1. Furthermore, in S30, the CPU 21 removes low-frequency components from the digital signal for the signal acquisition cycle acquired in S10.

Next, in S40, the CPU 21 subtracts the digital signal obtained in the process of S30 from the digital signal obtained in the process of S20.
Then, in S50, the CPU 21 calculates a concentration detection current value based on the digital signal obtained in the process of S40, and further, in S60, the CPU 21 calculates an element resistance value based on the digital signal obtained in the process of S30, and ends the concentration current detection process.

The microcomputer 7 of the gas sensor control device 1 configured in this manner is configured to acquire from the gas sensor 2 a concentration detection signal (i.e., the digital signal DS1 output from the A/D converter 17) whose value changes depending on the oxygen concentration, and to generate a high-frequency extraction signal by extracting high-frequency components from the acquired concentration detection signal.

The microcontroller 7 is configured to acquire a concentration detection signal from the gas sensor 2 and generate a delayed signal by delaying the acquired concentration detection signal by the delay time Td1 required to generate a high-frequency extraction signal.

The microcomputer 7 is configured to subtract the generated high frequency extraction signal from the generated delayed signal.
Such a microcomputer 7 can reduce noise superimposed on the concentration detection signal, and can suppress a decrease in the accuracy of gas concentration detection.

The microcomputer 7 is also configured to calculate the element resistance value of the sensor element 3 of the gas sensor 2 based on the generated high-frequency extraction signal. This allows the microcomputer 7 to detect the element resistance value of the sensor element 3.

In the embodiment described above, the microcontroller 7 corresponds to a concentration detection device, S30 corresponds to processing as a high frequency extraction unit, S20 corresponds to processing as a delay unit, S40 corresponds to processing as a subtraction unit, and S60 corresponds to processing as an element resistance calculation unit.

[Fourth embodiment]
A fourth embodiment of the present disclosure will be described below with reference to the drawings. In the fourth embodiment, differences from the third embodiment will be described. The same reference numerals will be used to designate the same components.

The gas sensor control apparatus 1 of the fourth embodiment differs from the third embodiment in that the concentration current detection process is changed.
The concentration current detection process of the fourth embodiment differs from the third embodiment in that the process of S45 is added, the process of S55 is executed instead of S50, and the process of S60 is omitted.

That is, as shown in FIG. 8, when the process of S40 is completed, the CPU 21 removes high-frequency components from the digital signal obtained by the process of S40 in S45. Then, the CPU 21 calculates the concentration detection current value based on the digital signal obtained by the process of S45 in S55, and ends the concentration current detection process.

The microcomputer 7 of the gas sensor control device 1 configured in this manner is further configured to extract low-frequency components from the subtraction signal generated by subtracting the high-frequency extraction signal from the delayed signal.

Such a microcontroller 7 can reduce noise superimposed on the concentration detection signal when the frequency range that can be extracted by processing S30 does not include the frequency of the element resistance current component C2, thereby preventing a decrease in the accuracy of gas concentration detection.

In the embodiment described above, step S45 corresponds to the process performed by the low-frequency extraction unit.
Although one embodiment of the present disclosure has been described above, the present disclosure is not limited to the above embodiment and can be implemented in various modified forms.

The gas sensor control device 1 and the method thereof described in the present disclosure may be realized by a dedicated computer provided by configuring a processor and a memory programmed to execute one or more functions embodied in a computer program. Alternatively, the gas sensor control device 1 and the method thereof described in the present disclosure may be realized by a dedicated computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the gas sensor control device 1 and the method thereof described in the present disclosure may be realized by one or more dedicated computers configured by combining a processor and a memory programmed to execute one or more functions with a processor configured with one or more hardware logic circuits. In addition, the computer program may be stored in a computer-readable non-transient tangible recording medium as instructions executed by a computer. The method for realizing the functions of each unit included in the gas sensor control device 1 does not necessarily need to include software, and all of the functions may be realized using one or more hardware.

Multiple functions possessed by one component in the above embodiments may be realized by multiple components, or one function possessed by one component may be realized by multiple components. Furthermore, multiple functions possessed by multiple components may be realized by one component, or one function realized by multiple components may be realized by one component. Furthermore, part of the configuration of the above embodiments may be omitted. Furthermore, at least part of the configuration of the above embodiments may be added to or substituted for the configuration of another of the above embodiments.

In addition to the gas sensor control device 1 described above, the present disclosure can be realized in various forms, such as a system including the gas sensor control device 1 as a component, a program for causing a computer to function as the gas sensor control device 1, a non-transient physical recording medium such as a semiconductor memory on which the program is recorded, and a concentration detection method.

2...Gas sensor, 3...Sensor element, 4...Heater, 7...Microcomputer, 30...Concentration current detection circuit, 31...Digital high-pass filter, 32...Delay circuit, 33...Subtractor

Claims (3)

a high-frequency extraction unit (31, S30) configured to acquire a concentration detection signal, the value of which changes in accordance with the concentration of a specific gas contained in a measurement gas, from a gas sensor (2) that detects the concentration of the specific gas contained in the measurement gas, and to generate a high-frequency extraction signal by extracting high-frequency components from the acquired concentration detection signal;
a delay unit (32, S20) configured to acquire the concentration detection signal from the gas sensor, and generate a delayed signal by delaying the acquired concentration detection signal by a high-frequency extraction processing time required for the high-frequency extraction unit to generate the high-frequency extraction signal;
a subtraction unit (33, S40) configured to subtract the high-frequency extraction signal generated by the high-frequency extraction unit from the delayed signal generated by the delay unit. 2. The concentration detection device according to claim 1, further comprising:
A concentration detection device comprising a low-frequency extraction unit (36, S45) configured to extract low-frequency components from a subtraction signal generated by the subtraction unit by subtracting the high-frequency extraction signal from the delayed signal. 2. The concentration detection device according to claim 1, further comprising:
A concentration detection device comprising: an element resistance calculation unit (35, S60) configured to calculate an element resistance value of a sensor element (3) provided in the gas sensor based on the high-frequency extraction signal generated by the high-frequency extraction unit.

Images