Air-fuel ratio sensor control device

Abstract

To reduce detection errors caused by offset while suppressing increase in circuit scale.SOLUTION: A terminal drive section 10 alternately switches an applied voltage of a first voltage value and an applied voltage of a second voltage value different from the first voltage value to an air-fuel ratio sensor at each predetermined sweeping period. A shunt resistor 15 outputs a detection voltage Vr1 corresponding to a current flowing through the air-fuel ratio sensor 2. A chopping switch 29 inputs the detection voltage Vr1, and alternately switches and outputs a voltage in which the detection voltage Vr1 is rotated forward and a voltage in which the detection voltage Vr1 is inverted for each predetermined chopping period. A control section 8 controls the operation of the chopping switch 29 and calculates an air-fuel ratio detected by the air-fuel ratio sensor based on the output voltage of the chopping switch 29. In the configuration, the chopping period is set to an integer multiple of the sweeping period, or at least two times.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an air-fuel ratio sensor control device for controlling an air-fuel ratio sensor. [Background technology]

[0002] As disclosed in Patent Document 1, an air-fuel ratio sensor control device that controls an air-fuel ratio sensor applies to the air-fuel ratio sensor a voltage that switches between high and low levels every predetermined sweep period, i.e., a square wave voltage, and detects the current output from the air-fuel ratio sensor at that time. The air-fuel ratio sensor control device then detects the air-fuel ratio based on the DC current, which is the direct current component of the current thus detected, and detects the impedance of the air-fuel ratio sensor based on the AC current, which is the alternating current component of the current. In this specification, the air-fuel ratio is sometimes referred to as A / F. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-7887 A Summary of the Invention [Problem to be solved by the invention]

[0004] In an air-fuel ratio sensor control device configured as described above, an offset in the configuration for detecting the current output from the air-fuel ratio sensor, specifically, an offset in the analog front end and the A / D converter, becomes an A / F detection error. Therefore, in an air-fuel ratio sensor control device, it is desirable to reduce such offset as much as possible. Note that in this specification, the analog front end may be abbreviated as AFE, and the A / D converter may be abbreviated as ADC.

[0005] Common offset cancellation technologies include, for example, the first technology, which uses a chopper amplifier in the AFE, the second technology, which uses an auto-zero amplifier in the AFE, and the third technology, which performs zero correction in the system. The first technology can achieve low offset and low noise. However, the first technology has some issues, such as a slight increase in circuit size, the need for fast chopping to allow the sweep signal to pass, and noise caused by the chopped signal.

[0006] The second technology can achieve low offset and low noise. However, the second technology has some issues, such as an increase in circuit size and an increase in noise due to control signals and aliasing. The third technology can eliminate the need for additional circuits. However, the third technology has some issues, such as difficulty in dynamic compensation and vulnerability to offset drift.

[0007] The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an air-fuel ratio sensor control device that can reduce detection errors caused by offsets while suppressing an increase in circuit size. [Means for solving the problem]

[0008] The air-fuel ratio sensor control device (5) according to claim 1 controls an air-fuel ratio sensor (2), and includes a voltage application unit (10), a current-voltage conversion unit (15), a chopping switch (29), and a control unit (8). The voltage application unit applies to the air-fuel ratio sensor a first voltage value and a second voltage value different from the first voltage value, by alternately switching between them for each predetermined sweep period. The current-voltage conversion unit outputs a detection voltage corresponding to a current flowing through the air-fuel ratio sensor. The chopping switch receives the detection voltage, and alternately switches between outputting a voltage obtained by forward inversion of the detection voltage and a voltage obtained by inverting the detection voltage, by alternately switching between them for each predetermined chopping period. The control unit controls the operation of the chopping switch, and calculates the air-fuel ratio detected by the air-fuel ratio sensor based on a detection signal obtained by amplifying and A / D converting the output voltage of the chopping switch. The control unit controls a demodulation unit (24) that outputs a signal obtained by demodulating the detection signal, and a control unit (8) that converts the output signal of the demodulation unit into a detection signal. By averaging Calculate the air-fuel ratio A calculation unit (26) .

[0009] In this way, the air-fuel ratio sensor control device according to claim 1 has a configuration in which a chopping switch is added to the air-fuel ratio sensor control device described in the prior art. In the above configuration, the chopping period is set to an integer multiple of two or more of the sweep period. In this way, the operation of switching the voltage output from the chopping switch, that is, the chopping operation by the chopping switch, is synchronized with the sweep period. Therefore, the offset in the configuration for detecting the current flowing through the air-fuel ratio sensor is offset in the voltage output from the chopping switch. Therefore, according to the above configuration, the offset can be compensated for without requiring a significant addition of a circuit configuration. In other words, according to the above configuration, the excellent effect of reducing detection errors caused by the offset while suppressing an increase in the circuit size can be obtained. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a schematic configuration of an A / F sensor system according to a first embodiment; [Diagram 2] FIG. 1 is a diagram showing an example of a specific configuration of an A / F sensor control device according to a first embodiment; [Diagram 3] FIG. 1 is a timing chart for explaining an example of an operation of the A / F sensor system according to the first embodiment; [Figure 4] FIG. 11 is a timing chart for explaining an example of the operation of the A / F sensor system according to the second embodiment; [Diagram 5] FIG. 11 is a timing chart for explaining an example of an operation of the A / F sensor system according to the first embodiment when the DC current has a negative value; [Figure 6] FIG. 1 is a timing chart for explaining an example of an operation of the A / F sensor system according to the first embodiment when the DC current has a positive value; [Figure 7] FIG. 11 is a timing chart for explaining an example of an operation of the A / F sensor system according to the second embodiment when the DC current has a negative value; [Figure 8] FIG. 11 is a timing chart for explaining an example of an operation of the A / F sensor system according to the second embodiment when the DC current has a positive value; [Figure 9] FIG. 13 is a diagram for explaining a specific application example of control executed by a control unit according to the third embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, a number of embodiments will be described with reference to the drawings. Note that the same reference numerals are used to designate substantially the same components in the respective embodiments, and the description thereof will be omitted. (First embodiment) The first embodiment will be described below with reference to FIGS.

[0012] As shown in Fig. 1, an A / F sensor system 1 of this embodiment is provided in an ECU, which is an electronic control unit mounted on a vehicle such as an automobile. The A / F sensor system 1 performs various control processes for detecting the A / F in the exhaust gas by an A / F sensor 2, using exhaust gas discharged by an internal combustion engine of the vehicle as the detection gas. In this case, a heater 3 is provided near the A / F sensor 2. The A / F sensor 2 is configured to be heated by the heater 3, for example, to about 800°C.

[0013] The A / F sensor system 1 includes an MCU 4 and an A / F sensor control device 5 configured as a semiconductor integrated circuit such as an ASIC. Note that MCU is an abbreviation for Micro Controller Unit, and ASIC is an abbreviation for Application Specific Integrated Circuit. The MCU 4 includes a CPU, ROM, RAM, etc., and the CPU executes a computer program stored in the ROM to execute processing corresponding to the computer program, thereby performing various controls and processes described below. The A / F sensor control device 5 controls the A / F sensor 2, and includes functional blocks such as an internal power supply 6, a communication unit 7, a control unit 8, a heater control unit 9, a terminal drive unit 10, and a sensor current detection unit 11.

[0014] The internal power supply 6 generates stable DC power using an external power supply supplied from outside the A / F sensor control device 5. The internal power supply 6 supplies the generated DC power to each functional block inside the A / F sensor control device 5. The communication unit 7 communicates with the MCU 4. When the communication unit 7 receives various commands from the MCU 4, it transmits these various commands to the control unit 8. Furthermore, when various information is provided to the communication unit 7 from the control unit 8, it transmits the various information to the MCU 4.

[0015] The heater control unit 9 is provided with a command signal Sa generated by the MCU 4 and related to the drive of the heater 3. Based on the command signal Sa, the heater control unit 9 generates a heater drive signal Sb for duty control of the drive of the heater 3. The heater drive signal Sb is a binary signal that commands the power supply to the heater 3 to be turned on when it is at a high level and commands the power supply to the heater 3 to be turned off when it is at a low level.

[0016] The heater drive signal Sb is provided to a heater drive unit 12 provided outside the A / F sensor control device 5. The heater drive unit 12 is composed of, for example, a MOS transistor. The MOS transistor of the heater drive unit 12 is on / off controlled based on the heater drive signal Sb. This controls the on / off of the electricity supply to the heater 3. The temperature of the A / F sensor 2 is increased by the heater control unit 9 controlling the on / off of the electricity supply to the heater 3. A current flows through the A / F sensor 2 according to the A / F of the exhaust gas and the voltage between its terminals.

[0017] The terminal driver 10 includes buffer amplifiers 13 and 14 which apply a voltage between the terminals of the A / F sensor 2 via output terminals P1 and P2. A voltage corresponding to the difference between the output voltages of the buffer amplifiers 13 and 14 is applied between the terminals of the A / F sensor 2. In this case, the terminal driver 10 alternately applies a first voltage value VH and a second voltage value VL different from the first voltage value VH to the A / F sensor 2 every predetermined sweep period Ta, and functions as a voltage application unit.

[0018] The sensor applied voltage, which is the voltage applied to the A / F sensor 2, is a square wave voltage. The operation of the terminal driver 10 is controlled by a controller 8. The controller 8 controls the operation of the terminal driver 10 so that the sensor applied voltage becomes an appropriate value based on the detected value of the impedance of the A / F sensor 2, which is detected as described below. A shunt resistor 15 is connected between the output terminal of the buffer amplifier 14 and output terminal P2. The shunt resistor 15 converts the current flowing through the A / F sensor 2 into a voltage, that is, performs I / V conversion. Note that in the following description, the current flowing through the A / F sensor 2 may be referred to as the sensor output current.

[0019] A detection voltage Vr1, which is a voltage between each terminal of the shunt resistor 15, is provided to the sensor current detection unit 11. In this case, the shunt resistor 15 outputs the detection voltage Vr1 corresponding to the sensor output current, and functions as a current-voltage conversion unit. The sensor current detection unit 11 detects the sensor output current based on the voltage between each terminal of the shunt resistor 15, i.e., the detection voltage Vr1. The sensor current detection unit 11 outputs a detection signal Cad that indicates the detection result of the sensor output current.

[0020] The detection signal Cad output from the sensor current detection unit 11 is provided to the control unit 8. Based on the detection signal Cad, the control unit 8 calculates the A / F detected by the A / F sensor 2 and the impedance of the A / F sensor 2. The control unit 8 includes a register 16, which stores various values ​​and the like used in the various processes and controls executed by the control unit 8.

[0021] As a specific configuration of the A / F sensor control device 5 for realizing the above-mentioned functions, for example, a configuration as shown in Fig. 2 can be adopted. As shown in Fig. 2, the control unit 8 has functional blocks such as voltage control units 21 and 22, a timing control unit 23, a demodulation unit 24, a low-pass filter 25, and a calculation unit 26. The terminal driving unit 10 has D / A converters 27 and 28 in addition to the above-mentioned buffer amplifiers 13 and 14. In this specification, the low-pass filter may be abbreviated as LPF, and the D / A converter may be abbreviated as DAC. The sensor current detection unit 11 has a chopping switch 29, a fully differential amplifier 30, a filter circuit 31, and an ADC 32.

[0022] The voltage control unit 21 provides the DAC 27 with a digital signal corresponding to the control voltage Vo1. The control voltage Vo1 is a DC voltage having a constant voltage value Vp, for example, as shown in FIG. 3. As a result, the control voltage Vo1, which is a DC voltage, is provided to one terminal of the A / F sensor 2 via the buffer amplifier 13 and the output terminal P1. The voltage control unit 22 provides the DAC 28 with a digital signal corresponding to the control voltage Vo2.

[0023] 3, the control voltage Vo2 is a pulse voltage that alternates between a first voltage value VH and a second voltage value VL for each sweep period Ta. As a result, the control voltage Vo2, which is a pulse voltage, is applied to the other terminal of the A / F sensor 2 via the buffer amplifier 14 and the output terminal P2. The operations of the voltage control units 21 and 22 are controlled by a timing control unit 23.

[0024] The voltage between the terminals of the shunt resistor 15, that is, the detection voltage Vr1, is applied to the chopping switch 29. The detection voltage Vr1 has a waveform, for example, as shown in Fig. 3. In Fig. 3, the detection voltage Vr1 is represented with the direction in which the sensor output current flows into the A / F sensor control device 5 being positive. The chopping switch 29 is formed of an analog circuit, which receives the detection voltage Vr1 and alternately switches between a voltage obtained by forward inversion of the detection voltage Vr1 and a voltage obtained by inverting the detection voltage Vr1 for each predetermined chopping period Tb, and outputs the voltage.

[0025] The operation of the chopping switch 29 is controlled by a chopping signal Vc output from a timing control unit 23 of the control unit 8. The chopping signal Vc is, for example, a binary signal as shown in Fig. 3. The chopping switch 29 outputs a voltage obtained by inverting the detection voltage Vr1 while the chopping signal Vc is at a high level, and outputs a voltage obtained by inverting the detection voltage Vr1 while the chopping signal Vc is at a low level. The timing control unit 23 controls the operations of the voltage control units 21 and 22 and the chopping switch 29 so that the chopping period Tb is an integer multiple of the sweep period Ta that is equal to or greater than two.

[0026] 3, in this embodiment, the chopping period Tb is set to twice the sweep period Ta, that is, "Tb=2×Ta." In this case, the edge of the chopping signal Vc is synchronized with the falling edge of the control voltage Vo2, whereby the chopping operation by the chopping switch 29 is synchronized with the sweep operation by the voltage control units 21 and 22. Note that the edge of the chopping signal Vc may be synchronized with the rising edge of the control voltage Vo2.

[0027] The detection voltage Vr2, which is the voltage output from the chopping switch 29, has a waveform, for example, as shown in Fig. 3. That is, the detection voltage Vr2 is approximately the same as the detection voltage Vr1 during the period when the chopping signal Vc is at a high level, and is approximately the same as the inverted voltage of the detection voltage Vr1 during the period when the chopping signal Vc is at a low level. The reason why the waveforms of the detection voltages Vr1 and Vr2 do not completely match is as follows. That is, the conversion from the detection voltage Vr1 to the detection voltage Vr2 is performed by an analog circuit, and settling at the switching timing of the chopping switch 29 is not completely in time, resulting in a slight difference in the waveforms of the detection voltages Vr1 and Vr2.

[0028] The detection voltage Vr2 output from the chopping switch 29 is input to the amplifier 30. The amplifier 30 amplifies the detection voltage Vr2 at a predetermined amplification factor and outputs the amplified voltage. The output voltage of the amplifier 30 is input to the ADC 32 via the filter circuit 31. The filter circuit 31 is a first-order CR filter composed of two resistors R1 and R2 and one capacitor C1. The voltage output from the filter circuit 31 becomes the input voltage Vin of the ADC 32. The input voltage Vin is a voltage obtained by amplifying the detection voltage Vr2 at a predetermined amplification factor, as shown in FIG. 3, for example. The ADC 32 converts the input voltage Vin into a digital signal and outputs it. The sensor current detection unit 11 outputs the digital signal output from the ADC 32 as a detection signal Cad.

[0029] The demodulation unit 24 receives the detection signal Cad and outputs a detection signal Cdm obtained by demodulating the detection signal Cad. The term "demodulation" used here refers to the operation of restoring the detection signal Cad to its original value, which has been inverted from its original value by the operation of the chopping switch 29. The operation of the demodulation unit 24 is controlled by the chopping signal Vc output from the timing control unit 23. Specifically, the demodulation unit 24 outputs a signal obtained by forwarding the detection signal Cad during a period in which the chopping signal Vc is at a high level, and outputs a signal obtained by inverting the detection signal Cad during a period in which the chopping signal Vc is at a low level.

[0030] The detection signal Cdm output from the demodulation unit 24 has a waveform, for example, as shown in Fig. 3. That is, the detection signal Cdm has the same waveform as the input voltage Vin, i.e., the detection signal Cad, during the period when the chopping signal Vc is at a high level, and has the same waveform as the inverted input voltage Vin, i.e., the detection signal Cad, during the period when the chopping signal Vc is at a low level. The detection signal Cdm output from the demodulation unit 24 is input to the LPF 25.

[0031] The LPF 25 is a digital filter, and outputs a signal from which high frequency components have been removed from the input detection signal Cdm. The calculation unit 26 calculates the A / F detected by the A / F sensor 2 and the impedance of the A / F sensor 2 based on the output signal of the LPF 25. The calculation unit 26 transmits data representing the calculated A / F and impedance to the MCU 4 via the communication unit 7. Thus, in the above configuration, the control unit 8 controls the operation of the chopping switch 29, and calculates the A / F detected by the A / F sensor 2 based on the output voltage of the chopping switch 29.

[0032] Next, a specific method of calculating the A / F and impedance by the calculation unit 26 will be described with reference to the timing chart of Fig. 3. First, the calculation unit 26 obtains various values ​​as follows by sampling and holding the output signal of the LPF 25. That is, during the period when the chopping signal Vc is at a high level, the calculation unit 26 converts the value represented by the detection signal Cdm into an input voltage at the timing immediately before the voltage control unit 22 changes and controls the control voltage Vo2 from the second voltage value VL to the first voltage value VH, that is, at the timing immediately before the rising edge of the control voltage Vo2, and obtains this as the AD conversion result ADLp.

[0033] The calculation unit 26 obtains, as the AD conversion result ADHp, a value represented by the detection signal Cdm converted into an input voltage during a period when the chopping signal Vc is at a high level, at a timing immediately before the voltage control unit 22 changes and controls the control voltage Vo2 from the first voltage value VH to the second voltage value VL, that is, at a timing immediately before the falling edge of the control voltage Vo2. The calculation unit 26 obtains, as the AD conversion result ADLm, a value represented by the detection signal Cdm converted into an input voltage during a period when the chopping signal Vc is at a low level, at a timing immediately before the rising edge of the control voltage Vo2. The calculation unit 26 obtains, as the AD conversion result ADHm, a value represented by the detection signal Cdm converted into an input voltage during a period when the chopping signal Vc is at a low level, at a timing immediately before the falling edge of the control voltage Vo2.

[0034] The calculation unit 26 calculates the A / F value by averaging four consecutive AD conversion results, etc. That is, in this case, the number of taps of the moving average in the A / F calculation is "4". Specifically, the calculation unit 26 uses the four consecutive AD conversion results ADHp, ADLp, ADHm, ADLm, etc. to calculate the current value Is of the DC current, which is the DC component of the sensor output current, based on the following formula (1), i.e., the A / F value. Here, G is the amplification factor of the amplifier 30, and Rs is the resistance value of the shunt resistor 15.

[0035]

number

[0036] The calculation unit 26 calculates ΔVad based on the following formula (2) using five consecutive AD conversion results ADHp, ADLm, ADHm, ADLp, and ADHp'. The AD conversion result ADHp' is another AD conversion result ADHp that is acquired first after the AD conversion result ADHp is acquired. The calculation unit 26 then calculates the impedance value Zac of the A / F sensor 2 based on the following formula (3) using the ΔVad calculated in this way. Here, ΔV is the amplitude of the sensor applied voltage, that is, the difference voltage between the first voltage value VH and the second voltage value VL.

[0037]

number

[0038] According to the present embodiment described above, the following effects can be obtained. The sensor current detection section 11 included in the A / F sensor control device 5 of this embodiment is provided with a chopping switch 29 that receives a detection voltage Vr1, which is the voltage between the terminals of the shunt resistor 15, and alternately switches between a voltage obtained by inverting the detection voltage Vr1 and a voltage obtained by inverting the detection voltage Vr1 every predetermined chopping period Tb. The control section 8 controls the operation of the chopping switch 29 and calculates the A / F detected by the A / F sensor 2 based on a detection signal Cad obtained by amplifying and A / D converting the detection voltage Vr2, which is the output voltage of the chopping switch 29.

[0039] In this way, the A / F sensor control device 5 of this embodiment has a configuration in which the chopping switch 29 is added to the air-fuel ratio sensor control device described in the prior art. In the above configuration, the chopping period Tb is set to an integer multiple of two or more of the sweep period Ta of the sensor applied voltage. In this way, the operation of switching the detection voltage Vr2 output from the chopping switch 29, that is, the chopping operation by the chopping switch 29, is synchronized with the sweep period Ta.

[0040] Therefore, in the detection voltage Vr2 output from the chopping switch 29, and in turn in the detection signal Cad, the offset in the detection system, such as the sensor current detection unit 11, which is a configuration for detecting the current flowing through the A / F sensor 2, specifically the amplifier 30 and the ADC 32, is offset. Therefore, according to the above configuration, the offset can be dynamically compensated for by simply adding the chopping switch 29 to the circuit configuration, in other words, without requiring a significant addition of circuit configuration. In other words, according to this embodiment, it is possible to obtain an excellent effect of reducing detection errors caused by the offset while suppressing an increase in the circuit size. Note that FIG. 3 illustrates the operation waveforms of each unit in the case of stoichiometry where the current value Is of the DC current is 0 A, that is, "Is=0 A". In the A / F sensor control device, higher accuracy is required for A / F detection at stoichiometry, and this embodiment makes it possible to meet such a requirement.

[0041] In this embodiment, the chopping period Tb is set to twice the sweep period Ta, and therefore the following effect is also obtained: In this case, the speed of the chopping operation by the chopping switch 29 is slower than that of the chopper amplifier used in the first technique described in the prior art, so that the effects of noise due to the chopping signal Vc serving as the control clock and residual offset due to feedthrough can be reduced, and as a result, the effect of reducing detection errors is enhanced.

[0042] Second embodiment The second embodiment will be described below with reference to FIGS. In the first embodiment, as shown in Fig. 3, a glitch, which is a whisker-like pulse that appears in the waveform of the demodulated detection signal Cdm, is asymmetric at the rising edge and the falling edge. Specifically, a glitch appears at the rising edge of the detection signal Cdm, but no glitch appears at the falling edge of the detection signal Cdm.

[0043] Therefore, in the first embodiment, if the settling error of the LPF 25 remains until the timing of sample and hold, the AD conversion results ADLp, ADLm obtained by sample and hold after the rising edge of the detection signal Cdm will be values ​​affected by glitches, but the AD conversion results ADHp, ADHm obtained by sample and hold after the falling edge of the detection signal Cdm will be original values ​​that are not affected by glitches. This may cause an error in the A / F value calculated by averaging these AD conversion results ADLp, ADLm, ADHp, ADHm.

[0044] In this embodiment, in order to improve on these points, the contents of the various timing controls performed by the timing control unit 23 of the control unit 8 and the contents of the various calculations performed by the calculation unit 26 are different from those of the first embodiment. Note that the configuration of the A / F sensor system 1 is common to the first embodiment, and will be described with reference to Figures 1 and 2. The timing control unit 23 of this embodiment controls the operations of the voltage control units 21, 22 and the chopping switch 29 so that the chopping period Tb is an odd multiple of the sweep period Ta.

[0045] 4, in this embodiment, the chopping period Tb is set to three times the sweep period Ta, that is, "Tb=3×Ta." In this case, the rising edge of the chopping signal Vc is synchronized with the falling edge of the control voltage Vo2, and the falling edge of the chopping signal Vc is synchronized with the rising edge of the control voltage Vo2, so that the chopping operation by the chopping switch 29 is synchronized with the sweep operation by the voltage control units 21 and 22. Note that the rising edge of the chopping signal Vc may be synchronized with the rising edge of the control voltage Vo2, and the falling edge of the chopping signal Vc may be synchronized with the falling edge of the control voltage Vo2.

[0046] Next, a specific method of calculating the A / F and impedance by the calculation unit 26 of this embodiment will be described with reference to the timing chart of Fig. 4. First, the calculation unit 26 obtains various values ​​as follows by sampling and holding the output signal of the LPF 25. That is, the calculation unit 26 obtains, as AD conversion results ADLp1 and ADLp2, the value represented by the detection signal Cdm converted into an input voltage at the timing immediately before the rising edge of the control voltage Vo2 during the period when the chopping signal Vc is at a high level.

[0047] The calculation unit 26 obtains, as the AD conversion result ADHp, a value represented by the detection signal Cdm converted into an input voltage at the timing immediately before the falling edge of the control voltage Vo2 during the period when the chopping signal Vc is at a high level. The calculation unit 26 obtains, as the AD conversion result ADHm1, ADHm2, a value represented by the detection signal Cdm converted into an input voltage at the timing immediately before the falling edge of the control voltage Vo2 during the period when the chopping signal Vc is at a low level. The calculation unit 26 obtains, as the AD conversion result ADLm, a value represented by the detection signal Cdm converted into an input voltage at the timing immediately before the rising edge of the control voltage Vo2 during the period when the chopping signal Vc is at a low level.

[0048] The calculation unit 26 calculates the A / F value by averaging six consecutive AD conversion results, etc. That is, in this case, the number of taps of the moving average in the A / F calculation is "6." Specifically, the calculation unit 26 uses six consecutive AD conversion results ADLp1, ADHp, ADLp2, ADHm1, ADLm, ADHm2, etc. to calculate the current value Is of the DC current, which is the DC component of the sensor output current, based on the following formula (4), i.e., the A / F value.

[0049]

number

[0050] The calculation unit 26 calculates ΔVad based on the following formula (5) using seven consecutive AD conversion results ADLp1, ADHp, ADLp2, ADHm1, ADLm, ADHm2, and ADLp1'. The AD conversion result ADLp1' is another AD conversion result ADLp1 that is acquired first after the AD conversion result ADLp1 is acquired. Then, the calculation unit 26 uses the ΔVad calculated in this way and the like to calculate the impedance value Zac of the A / F sensor 2 based on the formula (3) described in the first embodiment.

[0051]

number

[0052] In the present embodiment described above, as in the first embodiment, the chopping operation is synchronized with the sweep period Ta, so that offsets in the detection system, such as the amplifier 30 and the ADC 32, are offset in the detection voltage Vr2 output from the chopping switch 29, and in turn in the detection signal Cad. Therefore, in the present embodiment, too, it is possible to obtain the effect of reducing detection errors caused by offsets while suppressing an increase in the circuit size.

[0053] In this embodiment, the chopping period Tb is set to an odd multiple of the sweep period Ta, specifically, three times the sweep period Ta, so that the following effect can be obtained. That is, in this embodiment, as shown in Fig. 4, glitches appear in the demodulated detection signal Cdm at both the rising and falling edges. That is, in this embodiment, the glitches appearing in the waveform of the detection signal Cdm are symmetrical at the rising and falling edges of the detection signal Cdm.

[0054] Therefore, in this embodiment, the settling error, such as a long settling time of LPF 25, is suppressed from affecting the calculation of the A / F value, etc., and as a result, the detection error of the A / F value can be further reduced. Also, in this embodiment, because the effect of the settling error of LPF 25 on the calculation of the A / F value, etc. can be suppressed to be small in this way, it becomes possible to employ a filter having stronger filtering characteristics as LPF 25, and as a result, an effect is obtained in which noise resistance can be improved.

[0055] In the first embodiment, the influence of the glitch as described above becomes more prominent when the current value Is is not 0A, that is, when "Is ≒ 0A", but in this embodiment, this point is also improved. The contents of such improvements will be described below with reference to the timing charts of Figs. 5 to 8. Note that Fig. 5 shows the operation waveforms of each part when the current value Is is a negative value in the first embodiment, that is, when "Is < 0A", and Fig. 6 shows the operation waveforms of each part when the current value Is is a positive value in the first embodiment, that is, when "Is > 0A". Fig. 7 shows the operation waveforms of each part when "Is < 0A" in this embodiment, and Fig. 8 shows the operation waveforms of each part when "Is > 0A" in this embodiment.

[0056] As shown in FIG. 5 and FIG. 6, in the first embodiment, when the current value Is is a negative value, the glitch is larger than when the current value Is is a positive value, and the influence of the glitch is larger. Therefore, in the first embodiment, the influence of the glitch is not averaged when the current value Is is positive or negative, and the maximum value of the detection error is large. In the first embodiment, the influence of the glitch due to the chopping operation depends on the sign of the current value Is and the synchronization state of the sweep period Ta and the chopping period Tb. In contrast, as shown in FIG. 7 and FIG. 8, in this embodiment, when the absolute values ​​of the current value Is are equal, the influence of the glitch is equal when the current value Is is a negative value and when the current value Is is a positive value. Therefore, in this embodiment, the influence of the glitch is averaged when the current value Is is positive or negative, and the maximum value of the detection error is suppressed to be low.

[0057] Third embodiment The third embodiment will be described below with reference to FIG. In the configurations of the above embodiments, when the chopping operation by the chopping switch 29 is not performed, the configuration is equivalent to the configuration of the prior art. Hereinafter, such a configuration will be referred to as the conventional configuration. According to the conventional configuration, the real-time detection of the A / F value, i.e., the responsiveness, can be improved compared to the above embodiments in which the chopping operation is performed, but detection errors are more likely to occur. Also, according to the first embodiment, the chopping period Tb is shorter and the number of taps of the moving average in the A / F calculation is smaller than in the second embodiment, so that the responsiveness of the detection of the A / F value, etc. can be improved, but the effect of reducing detection errors is smaller.

[0058] That is, the detection responsiveness increases in the order of "Second embodiment" < "First embodiment" < "Conventional configuration", and the detection accuracy increases in the order of "Conventional configuration" < "First embodiment" < "Second embodiment". The allowable range of deterioration in detection responsiveness depends on the system. Generally, the sweep frequency, which is the frequency of the voltage applied to the sensor, is about several kHz, while the system responsiveness is several hundred Hz or less. Therefore, the detection responsiveness in the second embodiment is acceptable for a general system.

[0059] Considering these points, it is believed that it is possible to achieve both detection responsiveness and detection accuracy by combining the above-mentioned configurations. Therefore, in the third embodiment, the control unit 8 is configured to be able to enable or disable the operation of the chopping switch 29. In addition, the control unit 8 is configured to be able to variably set the chopping period Tb. In this case, the chopping period Tb is stored in the register 16, and its value is variable depending on the setting of the register 16.

[0060] Specifically, the control unit 8 is configured to be able to switch the chopping period Tb between a first period Tb1, which is the chopping period "Tb=2×Ta" in the first embodiment, and a second period Tb2, which is the chopping period "Tb=3×Ta" in the second embodiment. In addition, the control unit 8 is also configured to switch the number of taps of the moving average in the calculation, that is, the number of calculation taps, in response to such switching of the chopping period. In other words, in this embodiment, the control unit 8 is configured to dynamically switch the chopping period Tb and the number of calculation taps.

[0061] Next, a specific application example of this embodiment will be described with reference to the flowchart in Fig. 9. The control unit 8 executes the process shown in Fig. 9 at predetermined intervals. First, in step S100, the amount of accelerator depression is acquired. In this case, the control unit 8 is capable of determining the amount of accelerator depression in three stages, for example, "large," "medium," and "small." In step S200, it is determined whether the amount of accelerator depression is "large."

[0062] If it is determined that the accelerator depression amount is "large", the result in step S200 is "YES" and the process proceeds to step S300. In step S300, the operation of the chopping switch 29 is disabled, that is, "chopping operation = none" is set. After step S300 is executed, this process ends. On the other hand, if it is determined that the accelerator depression amount is "medium" or "small", the result in step S200 is "NO" and the process proceeds to step S400. In step S400, the operation of the chopping switch 29 is enabled, that is, "chopping operation = yes" is set.

[0063] After step S400 is executed, the process proceeds to step S500, where it is determined whether the accelerator depression amount is "medium". If it is determined that the accelerator depression amount is "medium", the result is "YES" in step S500, and the process proceeds to step S600. In step S600, the chopping period is set to the first period Tb1. On the other hand, if it is determined that the accelerator depression amount is "light", the result is "NO" in step S500, and the process proceeds to step S700. In step S700, the chopping period is set to the second period Tb2. After step S600 or S700 is executed, the process ends.

[0064] When the accelerator pedal is depressed heavily, the A / F value changes suddenly, so the calculation of the A / F value requires even greater real-timeness, but detection accuracy is not required to be very high. On the other hand, when the accelerator pedal is not depressed much, the A / F value is close to stoichiometry and does not change much, so the calculation of the A / F value requires extremely high accuracy, but real-time calculation is not required. Therefore, in the above application example, the chopping operation is switched on and off and the chopping period is switched according to the amount of accelerator depression.

[0065] Specifically, according to the above-mentioned application example, when the accelerator depression amount is "large", the chopping operation is not performed, so that the detection accuracy is reduced, but the detection responsiveness can be maximized. Also, according to the above-mentioned application example, when the accelerator depression amount is "small", the chopping operation is performed and the chopping period is set to the second period Tb2, so that the detection responsiveness is reduced, but the detection accuracy can be maximized. Also, according to the above-mentioned application example, when the accelerator depression amount is "medium", the chopping operation is performed and the chopping period is set to the first period Tb1, so that both the detection responsiveness and the detection accuracy can be increased to a required level.

[0066] As described above, in this embodiment, the control unit 8 can enable or disable the chopping operation, and can variably set the chopping period. That is, the control unit 8 of this embodiment dynamically switches between the presence and absence of the chopping operation, and switches the chopping period and the number of calculation taps. In this way, it is possible to achieve both detection responsiveness and detection accuracy, such that responsiveness is increased only for a necessary period while maintaining good detection accuracy.

[0067] (Other embodiments) The present invention is not limited to the embodiments described above and illustrated in the drawings, and can be modified, combined, or expanded in any manner without departing from the spirit and scope of the present invention. The numerical values ​​and the like shown in the above embodiments are merely examples and are not intended to be limiting.

[0068] The chopping period may be set to an integer multiple of two or more times the sweep period. For example, the chopping period may be set to an even multiple of four or more times the sweep period, such as four or six times the sweep period. In this case, the same effects as those in the first embodiment can be obtained. Also, for example, the chopping period may be set to an odd multiple of five or more times the sweep period, such as five or seven times the sweep period. In this case, the same effects as those in the second embodiment can be obtained.

[0069] Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0070] 1...A / F sensor system, 2...A / F sensor, 5...A / F sensor control device, 8...control unit, 10...terminal drive unit, 15...shunt resistor, 29...chopping switch

Claims

1. An air-fuel ratio sensor control device (5) for controlling an air-fuel ratio sensor (2), a voltage application unit (10) that applies a first voltage value and a second voltage value different from the first voltage value to the air-fuel ratio sensor by switching between them every predetermined sweep period; a current-voltage conversion unit (15) that outputs a detection voltage corresponding to a current flowing through the air-fuel ratio sensor; a chopping switch (29) that receives the detection voltage and alternately switches between a voltage obtained by inverting the detection voltage and a voltage obtained by inverting the detection voltage for each predetermined chopping period, and outputs the voltage; a control unit (8) that controls an operation of the chopping switch and calculates an air-fuel ratio detected by the air-fuel ratio sensor based on a detection signal obtained by amplifying and A / D converting an output voltage of the chopping switch; Equipped with the chopping period is set to an integer multiple of two or more of the sweep period, The control unit is a demodulation unit (24) for outputting a signal obtained by demodulating the detection signal; a calculation unit (26) for calculating the air-fuel ratio by averaging an output signal of the demodulation unit; An air-fuel ratio sensor control device comprising:

2. 2. An air-fuel ratio sensor control device according to claim 1, wherein the chopping period is set to twice the sweep period.

3. 2. An air-fuel ratio sensor control device according to claim 1, wherein the chopping period is set to an odd multiple of the sweep period.

4. 4. An air-fuel ratio sensor control device according to claim 3, wherein said chopping period is set to three times as long as said sweep period.

5. 5. The air-fuel ratio sensor control device according to claim 1, wherein the control unit is configured to be able to enable or disable the operation of the chopping switch.

6. 6. The air-fuel ratio sensor control device according to claim 1, wherein the control section is configured to be able to variably set the chopping period.

7. 7. The air-fuel ratio sensor control device according to claim 1, which is configured as a semiconductor integrated circuit.

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