JP2020051847A - Driving device for air-fuel ratio sensor - Google Patents

Abstract

To provide a driver for an air-fuel ratio sensor which can reduce a voltage stress on an air-fuel ratio sensor.SOLUTION: A driving device 1 drives an air-fuel ratio sensor 2 having an oxygen pump cell 2a connected between a terminal AFV and a terminal COM and a Nernst cell 2b between a terminal AFR and the terminal COM. The output terminals of a first operational amplifier 3 and a second operational amplifier 4 are connected to the terminal AFV and the terminal COM, respectively. when a microcomputer 9 is turned on, the microcomputer performs voltage application processing of applying a predetermined voltage to both ends of the oxygen pump cell 2a through the first operational amplifier 3 and the second operational amplifier 4 before dual drive of the air-fuel ratio sensor starts to be controlled.SELECTED DRAWING: Figure 1

Description

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

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

JP-A-2006-70883 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 at the stage of monitoring the sensor state before that, an unintended difference between both ends of the oxygen pump cell when measuring the Ip current. There is a problem that voltage is applied and stress is applied.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an air-fuel ratio sensor driving device capable of reducing voltage stress applied to the air-fuel ratio sensor.

  According to the air-fuel ratio sensor driving device of the first aspect, 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 provided. The provided air-fuel ratio sensor is the drive target. Output terminals of the first and second operational amplifiers are connected to a first terminal and a common terminal, respectively. The voltage control circuit performs a voltage application process of applying a predetermined voltage to both ends of the oxygen pump cell via the first and second operational amplifiers when the power is turned on and before the driving control of the air-fuel ratio sensor is started. Do. With such control, it is possible to prevent an unintended voltage difference from being applied to both ends of the oxygen pump cell. Therefore, voltage stress applied to the air-fuel ratio sensor can be reduced.

  According to the air-fuel ratio sensor driving device of the second aspect, 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 potentials at both ends of the oxygen pump cell can be determined at a stage before the timing at which the drive voltage for starting energization of the oxygen pump cell is applied.

FIG. 6 is a diagram illustrating a configuration of a driving device of an air-fuel ratio sensor and a driving control mode: IDLE according to the first embodiment. Diagram showing drive control mode by drive device: AF2_IDLE Diagram showing drive control mode by drive device: AF2_VSMON Diagram showing drive control mode by drive device: AF2_JUDGE Diagram showing drive control mode by drive device: AF2_NORM Flow chart showing processing corresponding to the transition of the control mode shown in FIGS. 2 to 6 FIG. 9 is a diagram illustrating a configuration of a driving device of an air-fuel ratio sensor according to a second embodiment. FIG. 13 is a diagram illustrating a configuration of a driving device of an air-fuel ratio sensor according to a third embodiment.

(1st Embodiment)
As shown in FIG. 1, a drive device 1 of the present embodiment is driven by 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 an exhaust passage of an engine of a vehicle. In the air-fuel ratio sensor 2, the pump cell 2a is driven such that the output voltage of the electromotive force cell 2b according to the oxygen concentration difference between the diffusion chamber into which the exhaust gas is introduced and the reference oxygen chamber becomes the target value, and flows into the pump cell 2a. The current is measured as a sensor current that indicates the air-fuel ratio.

  The terminal AFC of the driving device 1 is connected to the negative terminal COM common to the pump cell 2a and the electromotive force cell 2b, the terminal AFV is connected to the positive terminal Ip + of the pump cell 2a, and the terminal AFR is connected to the positive terminal of the electromotive cell 2b. It is connected to the side terminal VS +. The terminal AFC corresponds to a common terminal, the terminal AFV corresponds to a first terminal, and the terminal AFR corresponds to a 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 generation circuit 5 is configured by a series circuit of resistance elements 5a and 5b connected between the power supply and the ground. The common connection point of the resistance elements 5a and 5b is connected to the non-inverting input terminal of the first operational amplifier 3 via the first switch 10.

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

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

  The microcomputer 9 inputs voltage data to an input terminal of the D / A converter 6 and controls on / off of each of the switches 10 to 13, 15, and 16. The microcomputer 9 also controls the operations of the constant current circuit 7 and the current application circuit 8. The driving device 1 includes, for example, an operational amplifier that amplifies the voltage between both ends of the resistance element 14, an A / D converter that converts the output voltage of the operational amplifier into an analog signal and inputs the converted voltage to the microcomputer 9, as in Patent Document 2. Although they are provided, they are not shown. The microcomputer 9 corresponds to a voltage control circuit. Further, the constant current circuit 7, the current application circuit 8, and the microcomputer 9 correspond to a current control circuit.

Next, the operation of the present 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 power is supplied to the driving device 1. In this state, the 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 applied voltage control is performed on the oxygen pump cell 2a of the air-fuel ratio sensor 2 (FIG. 6, S1). The reference voltage generated by the reference voltage generation circuit 5 is, for example, 2.5 V, and the microcomputer 9 supplies voltage data to the D / A converter 6 to output 2.5 V. Then, 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 to both ends of 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 small constant current Icp to the terminal AFR (S2). As a result, electricity is supplied to the Nernst cell 2b, 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 on / off of the switches 10 to 12, these are not shown.

<4: AF2_JUDGE>
In the mode AF2_JUDGE shown in FIG. 4, the microcomputer 9 operates the current sweep circuit 8 to perform current sweep from the terminal AFR. Then, when the terminal voltage of the resistance element 14 is A / D converted and read and the amount of change in the voltage between both ends of the electromotive force cell 2b is detected, the impedance Zac of the electromotive force cell 2b is obtained from the amount of change in the 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) is satisfied (YES), the process shifts to the next control mode to start the air-fuel ratio control (S6). Note that the mode AF2_VSMON to AF2_JUDGE corresponds 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 the air-fuel ratio control so that the voltage between the terminals AFR and AFC becomes 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). 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 activate again, and the process proceeds to step S3. That is, the control mode changes to AF2_JUDGE.

  As described above, according to the present 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 to be driven. The output terminals of the first and second operational amplifiers 3 and 4 are connected to the terminal AFV and the terminal COM, respectively. When the power is turned on, the microcomputer 9 outputs the first and second operational amplifiers before starting the two-drive control of the air-fuel ratio sensor. A voltage application process for applying a predetermined voltage to both ends of the oxygen pump cell 2a via the first and second operational amplifiers 3 and 4 is performed.

  Specifically, the reference voltage generation circuit 5, a first switch 10 disposed between the output terminal of the reference voltage generation circuit 5 and the non-inverting input terminal of the first operational amplifier 3, a D / A converter 6, A second switch 11 arranged between an output terminal of the D / A converter 6 and a non-inverting input terminal of the first operational amplifier 3; an output terminal of the D / A converter 6 and a non-inverting input terminal of the second operational amplifier 4; The microcomputer 9 supplies voltage data to be input to the D / A converter 6 and controls on / off of the first to third switches 10 to 12 to perform a voltage application process. Do. With such control, it is possible to avoid applying an unintended difference voltage to both ends of the oxygen pump cell 2a. Therefore, voltage stress applied to the air-fuel ratio sensor 2 can be reduced.

  Further, since the microcomputer 9 starts energization to the oxygen pump cell 2a via the terminal AFR after performing the voltage application process, the microcomputer 9 performs timing more than the timing at which the drive voltage for starting energization to the oxygen pump cell 2a is applied. At the previous stage, the potential at both ends of the oxygen pump cell 2a can be determined.

(2nd Embodiment)
Hereinafter, the same portions as those of the first embodiment will be denoted by the same reference numerals, and the description thereof will be omitted, and different portions will be described. As shown in FIG. 7, the driving device 21 of the second embodiment has a CR filter 22 disposed between the first switch 10 and the non-inverting input terminal of the first operational amplifier 3. Thus, high-frequency noise generated when the voltage output from the D / A converter 6 changes can be removed.

  In the second embodiment, when the applied voltage control is performed on 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 from the D / A converter 6 is applied to the non-inverting input terminals of the operational amplifiers 3 and 4. According to the second embodiment, the same effects as those of the first embodiment can be obtained. In this case, the output voltage of the D / A converter 6 does not have to be 2.5 V.

(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. The 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, the switches 10 to 12 are turned on and the switch 24 is turned off, so that the reference voltage generated by the reference voltage generating circuit 5 can be changed to the first voltage 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 a 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 in the same manner as in the first embodiment.
The number of drive control modes does not necessarily need to be five.
The voltage, the number of bits of the D / A converter, and the like may be appropriately changed according to individual designs.
Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments and the structures. The present disclosure also encompasses various modifications and variations within an equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more or less, are also included in the scope and concept of the present disclosure.

  In the drawing, 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 generating circuit, 6 is a D / A converter, 7 is a constant current circuit, 8 is a current application circuit, 9 is a microcomputer, 10 to 12 are first to third switches, and 15, 16 are fourth and fifth switches.

Claims (6)

An oxygen pump cell (2a) connected between the first terminal (AFV) and the common terminal (AFC), and an electromotive force cell (2b) connected between the second terminal (AFR) and the common terminal. The driving target is the air-fuel ratio sensor (2) provided.
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 a voltage applied to each of 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 a predetermined voltage to both ends of the oxygen pump cell before the drive control of the air-fuel ratio sensor is started. apparatus. A current control circuit (7, 8) for controlling a current supplied to the oxygen pump cell via the second terminal;
2. The air-fuel ratio sensor driving device according to claim 1, wherein the current control circuit starts energizing the oxygen pump cell after the voltage control circuit performs the voltage application process. 3. A reference voltage generation circuit (5) for generating a reference voltage;
A first switch (11) disposed between an output terminal of the reference voltage generation circuit and an input terminal of the first operational amplifier;
A D / A converter (6);
A second switch (12) disposed between an output terminal of the D / A converter and an input terminal of the first operational amplifier;
A third switch (13) disposed between an output terminal of the D / A converter and an 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 supplies voltage data to be input to the D / A converter, and controls the on / off of the first to third switches to perform the voltage application process. apparatus.   4. The air-fuel ratio sensor driving device according to claim 3, wherein the voltage control circuit causes the D / A converter to output the reference voltage and turns on the first and third switches to perform the voltage application process.   4. The air-fuel ratio sensor driving device according to claim 3, wherein the voltage control circuit causes the D / A converter to output a predetermined voltage and turns on the second and third switches to perform the voltage application process. A fourth switch (24) disposed between the output terminal of the D / A converter and the second and third switches;
4. The air-fuel ratio sensor driving device according to claim 3, wherein the voltage control circuit performs the voltage application process by turning on the first to third switches and turning off the fourth switch. 5.

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