JP7144733B2 - Drive device for air-fuel ratio sensor - Google Patents

Description

The present invention relates to a device for driving an air-fuel ratio sensor comprising an oxygen pump cell and an electromotive force cell.

In a device that drives an air-fuel ratio sensor that has an oxygen pump cell and an electromotive force cell, voltage is applied to these cells through an amplifier. A voltage is applied to the oxygen pump cell when measuring the O ₂ pumping current, the so-called Ip current.

JP 2016-70883 A JP 2018-105765 A

However, if the output of the amplifier connected to one end of the oxygen pump cell is in a high-impedance state during the previous sensor state monitoring stage, an unintended difference across the oxygen pump cell when measuring the Ip current. There is a problem that voltage is applied and stress is applied.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an air-fuel ratio sensor driving device capable of reducing the voltage stress applied to the air-fuel ratio sensor.

According to the air-fuel ratio sensor drive device of claim 1, the oxygen pump cell connected between the first terminal and the common terminal, and the electromotive force cell connected between the second terminal and the common terminal are The provided air-fuel ratio sensor is to be driven. Output terminals of the first and second operational amplifiers are connected to the first terminal and the common terminal, respectively. When the power is turned on, the voltage control circuit applies a predetermined voltage to the first terminal and the common terminal through the first and second operational amplifiers before the drive control of the air-fuel ratio sensor is started. process. By controlling in this manner, application of an unintended differential voltage across the oxygen pump cell can be avoided. Therefore, the voltage stress applied to the air-fuel ratio sensor can be reduced.

According to the air-fuel ratio sensor drive device of claim 2, the current control circuit starts energizing the oxygen pump cell via the second terminal after the voltage control circuit performs the voltage application process. With this configuration, the potential across the oxygen pump cell can be established before the timing of applying the driving voltage for starting the energization of the oxygen pump cell.

1 is a diagram showing the configuration of an air-fuel ratio sensor drive device and a drive control mode: IDLE, which is the first embodiment; Drive control mode by drive device: Diagram showing AF2_IDLE Drive control mode by drive device: Diagram showing AF2_VSMON Drive control mode by drive device: Diagram showing AF2_JUDGE Drive control mode by drive device: Diagram showing AF2_NORM Flowchart showing processing corresponding to control mode transitions shown in FIGS. 2 to 6 A diagram showing the configuration of an air-fuel ratio sensor drive device according to a second embodiment. A diagram showing the configuration of a drive device for an air-fuel ratio sensor according to a third embodiment.

(First embodiment)
As shown in FIG. 1, the driving device 1 of this embodiment drives an air-fuel ratio sensor 2 for detecting an air-fuel ratio. The air-fuel ratio sensor 2 is a two-cell type sensor having an oxygen pump cell 2a and a Nernst cell 2b corresponding to an electromotive force cell, and is arranged in the exhaust passage of the engine of the vehicle. In the air-fuel ratio sensor 2, the pump cell 2a is driven so that the output voltage of the electromotive force cell 2b corresponding to the oxygen concentration difference between the diffusion chamber into which the exhaust gas is introduced and the reference oxygen chamber becomes a target value, and the air flows through the pump cell 2a. Current is measured as a sensor current indicative of air-fuel ratio.

A terminal AFC provided in the driving device 1 is connected to a negative terminal COM common to the pump cell 2a and the electromotive force cell 2b, a terminal AFV is connected to the positive terminal Ip+ of the pump cell 2a, and a terminal AFR is connected to the positive terminal of the electromotive force cell 2b. side terminal VS+. The terminal AFC corresponds to the common terminal, the terminal AFV to the first terminal, and the terminal AFR to the second terminal.

The driving device 1 includes a first operational amplifier 3, a second operational amplifier 4, a reference voltage generating circuit 5, a D/A converter 6, a constant current circuit 7, a current applying circuit 8 and a microcomputer 9. The reference voltage generating circuit 5 is composed of a series circuit of resistance elements 5a and 5b connected between the power supply and the ground. A common connection point of the resistance elements 5 a and 5 b is connected to the non-inverting input terminal of the first operational amplifier 3 via the first switch 10 .

For example, the output terminal of the 14-bit D/A converter 6 is connected to the non-inverting input terminal of the first operational amplifier 3 via the second switch 11, and the output terminal of the second operational amplifier 4 via the third switch 12. Connected to the non-inverting input terminal. The output terminal of the first operational amplifier 3 is connected to the terminal AFV via the resistance element 13, and the output terminal of the second operational amplifier 4 is connected to the terminal AFC via the resistance element 14. FIG. The inverting input terminal of the second operational amplifier 4 is connected to the output terminal of the second operational amplifier 4 . The inverting input terminal of the first operational amplifier 3 is connected through the fourth switch 15 to the output terminal of the first operational amplifier 3 and through the fifth switch 16 to the terminal AFC.

A constant current circuit 7 supplies a constant current to the terminal AFR for generating an electromotive force in the Nernst cell 2b. The current application circuit 8 supplies constant currents flowing in opposite directions to the terminal AFR. In this embodiment, the constant currents in opposite directions are set to the same value, but they may be different.

The microcomputer 9 inputs voltage data to the input terminal of the D/A converter 6 and controls ON/OFF of each of the switches 10-13, 15 and 16. FIG. The microcomputer 9 also controls operations of the constant current circuit 7 and the current applying circuit 8 . The driving device 1 also includes an operational amplifier that amplifies the voltage across the resistance element 14 and an A/D converter that converts the output voltage of the operational amplifier into a digital signal and inputs it to the microcomputer 9, for example, as in Patent Document 2. Although provided, illustration of these is omitted. The microcomputer 9 corresponds to a voltage control circuit. The constant current circuit 7, current application circuit 8 and microcomputer 9 correspond to a current control circuit.

Next, the operation of this embodiment will be described. As shown in FIGS. 1 to 5, the drive control of the air-fuel ratio sensor 2 by the drive device 1 has, for example, five modes.
<1: IDLE>
The mode IDLE shown in FIG. 1 is a state immediately after the driving device 1 is powered on. In this state, switches 10, 12 and 16 are off. The output terminals of the operational amplifiers 3 and 4 are both high impedance; HiZ.

<2: AF2_IDLE>
In the mode AF2_IDLE shown in FIG. 2, the voltage applied to the oxygen pump cell 2a of the air-fuel ratio sensor 2 is controlled (FIG. 6, S1). The reference voltage generated by the reference voltage generating circuit 5 is, for example, 2.5V, and the microcomputer 9 supplies voltage data to the D/A converter 6 to output 2.5V. By turning on the switches 10 and 12 and turning off the switch 11, 2.5 V is input to the non-inverting input terminals of the operational amplifiers 3 and 4, respectively, and each voltage is applied across the oxygen pump cell 2a.

<3: AF2_VSMON>
In the mode AF2_VSMON shown in FIG. 3, the microcomputer 9 operates the constant current circuit 7 to supply a minute constant current Icp to the terminal AFR (S2). As a result, the Nernst cell 2b is energized, and a constant oxygen partial pressure state is always formed. At this time, the current flows according to the impedance of the air-fuel ratio sensor 2 . In the modes shown in FIGS. 3 to 5, since there is no change in the ON/OFF state of the switches 10 to 12, illustration of these is omitted.

<4: AF2_JUDGE>
In the mode AF2_JUDGE shown in FIG. 4, the microcomputer 9 operates the current sweep circuit 8 to sweep current from the terminal AFR. Then, when the terminal voltage of the resistance element 14 is A/D converted and read to detect the amount of change in the voltage across the electromotive force cell 2b, the impedance Zac of the electromotive force cell 2b is determined from the amount of change in voltage and the sweep current value. is calculated (S3).

Subsequently, the microcomputer 9 compares the impedance Zac with the threshold value N, and if (Zac≧N) (S4; NO), continues the current sweep (S5). When (Zac<N) (YES), the control mode is shifted to the next control mode and the air-fuel ratio control is started (S6). Modes AF2_VSMON to AF2_JUDGE correspond to an activation waiting period until the air-fuel ratio sensor 2 is activated.

<5: AF2_NORM>
In the mode AF2_NORM shown in FIG. 5, the microcomputer 9 performs air-fuel ratio control so that the voltage between the terminals AFR and AFC is constant. Here, the microcomputer 9 turns off the switch 15 and turns on the switch 16 . The same processing as steps S5 and S4 is performed (S7, S8), and when (Zac<N) (S8; YES), the air-fuel ratio is measured (S9). Then, if the stop command is not issued (S10; NO), the process returns to step S7 to continue the air-fuel ratio control.

If (Zac≧N) in step S8 (NO), it is determined that the temperature of the air-fuel ratio sensor 2 has decreased and it is necessary to reactivate it, and the process proceeds to step S3. That is, the control mode transitions to AF2_JUDGE.

As described above, according to this embodiment, the driving device 1 includes the oxygen pump cell 2a connected between the terminal AFV and the terminal COM, and the Nernst cell 2b connected between the terminal AFR and the terminal COM. The air-fuel ratio sensor 2 is assumed to be driven. The output terminals of the first and second operational amplifiers 3 and 4 are connected to the terminals AFV and COM, respectively. A voltage application process is performed to apply a predetermined voltage to both ends of the oxygen pump cell 2a through the first and second operational amplifiers 3 and 4, respectively.

Specifically, the reference voltage generation circuit 5, the first switch 10 arranged between the output terminal of the reference voltage generation circuit 5 and the non-inverting input terminal of the first operational amplifier 3, the D/A converter 6, a second switch 11 arranged between the output terminal of the D/A converter 6 and the non-inverting input terminal of the first operational amplifier 3; The microcomputer 9 supplies voltage data to be input to the D/A converter 6 and controls the on/off of the first to third switches 10 to 12 to perform voltage application processing. conduct. By controlling in this way, it is possible to avoid applying an unintended differential voltage across the oxygen pump cell 2a. Therefore, the voltage stress applied to the air-fuel ratio sensor 2 can be reduced.

In addition, since the microcomputer 9 starts energizing the oxygen pump cell 2a via the terminal AFR after performing the voltage application process, the timing is earlier than the timing at which the drive voltage for starting energizing the oxygen pump cell 2a is applied. At an earlier stage, the potential across the oxygen pump cell 2a can be established.

(Second embodiment)
Hereinafter, the same parts as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted, and different parts will be described. As shown in FIG. 7, the driving device 21 of the second embodiment has a CR filter 22 arranged between the first switch 10 and the non-inverting input terminal of the first operational amplifier 3 . As a result, high-frequency noise generated when the voltage output from the D/A converter 6 changes can be removed.

Further, in the second embodiment, when applying voltage control to the oxygen pump cell 2a in the drive control mode AF2_IDLE, the switch 10 is turned off and the switches 11 and 12 are turned on. As a result, the voltage of 2.5 V output by the D/A converter 6 is applied to the non-inverting input terminals of the operational amplifiers 3 and 4 . The same effects as those of the first embodiment can be obtained in the case of the second embodiment as described above. In this case, the output voltage of the D/A converter 6 does not have to be 2.5V.

(Third Embodiment)
As shown in FIG. 8, the driving device 23 of the third embodiment is obtained by adding a sixth switch 24 to the driving device 21 of the second embodiment. A sixth switch 24 is arranged between the output terminal of the D/A converter 6 and the common terminal of the switches 11 and 12 . As shown in the figure, by turning on the switches 10 to 12 and turning off the switch 24, the reference voltage generated by the reference voltage generation circuit 5 can be changed to the first and second voltages without using the D/A converter 6. It can be applied to the non-inverting input terminals of the second operational amplifiers 3 and 4 . The sixth switch 24 corresponds to the fourth switch in the claims.

(Other embodiments)
The CR filter 22 may be added to the configuration of the first embodiment, or the CR filter 22 may be deleted from the configurations of the second and third embodiments.
In the second and third embodiments, the drive control mode AF2_IDLE may be performed similarly to the first embodiment.
The number of drive control modes does not necessarily have to be five.
The voltage, the number of bits of the D/A converter, etc. may be appropriately changed according to the individual design.
Although the present disclosure has been described with reference to examples, it is understood that the present disclosure is not limited to such examples or structures. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and configurations, as well as other combinations and configurations, including single elements, more, or less, are within the scope and spirit of this disclosure.

In the drawings, 1 is a driving device, 2 is an air-fuel ratio sensor, 2a is an oxygen pump cell, 2b is a Nernst cell, 3 is a first operational amplifier, 4 is a second operational amplifier, 5 is a reference voltage generation circuit, 6 is a D/A converter, 7 is a constant current circuit, 8 is a current applying circuit, 9 is a microcomputer, 10 to 12 are first to third switches, and 15 and 16 are fourth and fifth switches.

Claims (6)

an oxygen pump cell (2a) connected between a first terminal (AFV) and a common terminal (AFC), and an electromotive force cell (2b) connected between a second terminal (AFR) and said common terminal The air-fuel ratio sensor (2) provided is driven,
a first operational amplifier (3) having an output terminal connected to the first terminal;
a second operational amplifier (4) having an output terminal connected to the common terminal;
a voltage control circuit (5, 6, 9) for controlling voltages applied to the first terminal and the common terminal via the first and second operational amplifiers;
When the power is turned on, the voltage control circuit performs a voltage application process of applying predetermined voltages to the first terminal and the common terminal before driving control of the air-fuel ratio sensor is started. Sensor drive. a current control circuit (7, 8) for controlling current supplied to the oxygen pump cell via the second terminal;
2. A drive device for an air-fuel ratio sensor according to claim 1, wherein said current control circuit starts energizing said oxygen pump cell after said voltage control circuit performs said voltage application process. a reference voltage generation circuit (5) for generating a reference voltage;
a first switch (1 0 ) arranged between the output terminal of the reference voltage generating circuit and the input terminal of the first operational amplifier;
a D/A converter (6);
a second switch (1 1 ) arranged between the output terminal of the D/A converter and the input terminal of the first operational amplifier;
a third switch (1 2 ) arranged between the output terminal of the D/A converter and the input terminal of the second operational amplifier;
3. The driving of the air-fuel ratio sensor according to claim 1, wherein the voltage control circuit provides voltage data to be input to the D/A converter, controls on/off of the first to third switches, and performs the voltage application process. Device. 4. A device for driving an air-fuel ratio sensor according to claim 3, wherein said voltage control circuit causes said D/A converter to output said reference voltage and turns on said first and third switches to perform said voltage application process. 4. The air-fuel ratio sensor drive device according to claim 3, wherein said voltage control circuit causes said D/A converter to output a predetermined voltage and turns on said second and third switches to perform said voltage application process. a fourth switch (24) arranged between the output terminal of the D/A converter and the second and third switches;
4. The air-fuel ratio sensor drive device according to claim 3, wherein the voltage control circuit turns on the first to third switches and turns off the fourth switch to perform the voltage application process.

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