JP2015206270A - Output correction method of oxygen sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an output correction method which corrects an output of an oxygen sensor when displacement is generated at an output characteristic of the oxygen sensor.SOLUTION: An output correction method of an oxygen sensor comprises: a first step for storing an output voltage of the oxygen sensor during fuel cut control, and an output voltage of the oxygen sensor during fuel rich control as a lean voltage for determining whether or not an air-fuel ratio is at a lean side at a prescribed value or larger, and a rich voltage for determining whether or not the air-fuel ratio is at a rich side at a prescribed value or larger; and a second step for performing correction for subtracting a value which is obtained by multiplying one half to a total sum of increase amounts of the rich voltage and the lean voltage from the output voltage of the oxygen sensor when a difference between the rich voltage and the lean voltage is not smaller than a first prescribed valve, the rich voltage and the lean voltage are increased by a second prescribed value with respect to a preset rich voltage and a preset lean voltage, and a difference of the increase amounts of the rich voltage and the lean voltage is not larger than a third prescribed value.

Description

  The present invention relates to an output correction method for an oxygen sensor.

  2. Description of the Related Art Conventionally, an oxygen sensor that detects a residual oxygen concentration in exhaust gas of an engine such as an automobile is known (for example, Patent Document 1). The oxygen sensor directly detects the oxygen concentration (oxygen partial pressure) in the exhaust gas, and the relationship between the oxygen concentration in the exhaust gas and the mixture ratio (air-fuel ratio) of air and fuel in the combustion chamber of the engine. Based on this, the air-fuel ratio can be detected.

  In an engine such as an automobile, the fuel injection amount is increased when the air-fuel ratio is larger than the stoichiometric air-fuel ratio (lean) based on the output voltage from the oxygen sensor, and when the air-fuel ratio is smaller than the stoichiometric air-fuel ratio (rich). In many cases, the fuel injection amount is reduced so that the air-fuel ratio is controlled to be within an appropriate range near the stoichiometric air-fuel ratio. Thereby, in the exhaust gas purification system using a three-way catalyst, the exhaust gas (HC, CO, NOx, etc.) purification rate can be maintained high.

  The oxygen sensor causes a steep electromotive force change (about 1 V) around the theoretical air-fuel ratio. Specifically, when the air-fuel ratio is on the lean side, the output voltage of the oxygen sensor shows a value in the vicinity of 0 V, but the output voltage of the oxygen sensor greatly increases near the stoichiometric air-fuel ratio, and the air-fuel ratio is on the rich side. In this case, the output voltage of the oxygen sensor is about 1V. In this way, the oxygen sensor outputs different voltage values depending on the stoichiometric air-fuel ratio when the air-fuel ratio is on the rich side and when the air-fuel ratio is on the lean side. It can be determined whether it is on the lean side or in an appropriate range near the stoichiometric air-fuel ratio.

JP 2003-202316 A

  However, there may be a deviation (offset) in the output characteristics of the oxygen sensor due to some factor. That is, the output voltage of the oxygen sensor is electrically offset, and may be output as a larger value than usual, for example. In such a case, a voltage different from the output voltage previously assumed as the output characteristic of the oxygen sensor is output from the oxygen sensor corresponding to the air-fuel ratio. Therefore, for example, even if the air-fuel ratio is in the appropriate range near the stoichiometric air-fuel ratio, an abnormality is detected if the air-fuel ratio is on the rich side more than a predetermined value, and as a result, the engine air-fuel ratio control can be performed appropriately. There is a risk of not.

  In view of the above problems, an oxygen sensor output correction method capable of correcting the output of an oxygen sensor in response to a shift in output characteristics when a shift occurs in the output characteristics of the oxygen sensor is provided. With the goal.

In order to solve the above problem, in one embodiment, an output correction method for an oxygen sensor includes:
An output correction method for an oxygen sensor attached to an exhaust pipe of an internal combustion engine,
A lean voltage for determining whether or not the air-fuel ratio in the combustion chamber of the internal combustion engine is on the fuel lean side with respect to the stoichiometric air-fuel ratio, and the air-fuel ratio with respect to the stoichiometric air-fuel ratio, As the rich voltage for determining whether or not the fuel rich side is greater than or equal to a predetermined value, the output voltage of the oxygen sensor during fuel cut control of the internal combustion engine, and the output of the oxygen sensor during fuel rich control of the internal combustion engine A first step of storing an output voltage;
The difference between the rich voltage and the lean voltage is equal to or greater than a first predetermined value, and the rich voltage and the lean voltage are increased by a second predetermined value or more with respect to a preset rich voltage and lean voltage. And when the difference between the rich voltage and the increase in the lean voltage is equal to or smaller than a third predetermined value, a value obtained by multiplying the sum of the increase in the rich voltage and the lean voltage by 1/2. And a second step of performing correction for subtracting from the output voltage of the oxygen sensor.

  According to the above-described embodiment, it is possible to provide an output correction method for an oxygen sensor that can correct the output of the oxygen sensor in response to the shift in the output characteristics when the output characteristics of the oxygen sensor have shifted. .

It is a block diagram which shows an example of a structure of the engine control apparatus which concerns on this embodiment. It is a flowchart which shows the output correction process of the oxygen sensor by the engine control apparatus (engine ECU) which concerns on this embodiment.

  Hereinafter, embodiments for carrying out the invention will be described with reference to the drawings.

  FIG. 1 is a block diagram illustrating an example of an engine control device 1 according to the present embodiment. The engine control device 1 is mounted on a vehicle and controls the engine 10 as a driving force source of the vehicle.

  The engine control device 1 includes an engine 10, an engine ECU 20, an oxygen sensor 30, and the like.

  The engine 10 is, for example, an internal combustion engine that is driven by using gasoline as fuel.

  The engine ECU 20 is an electronic control unit that controls the engine 10. The engine ECU 20 is configured by, for example, a microcomputer, and may execute various control processes by causing a control program in the internal memory to be executed on the CPU. Specifically, the air-fuel ratio control of the engine 10 is executed based on the output voltage corresponding to the air-fuel ratio of the engine 10 input from the oxygen sensor 30 (the mixing ratio of air and fuel in the combustion chamber of the engine 10). Good. For example, the engine ECU 20 sets the air-fuel ratio of the engine 10 near the stoichiometric air-fuel ratio (14.7 when the fuel is gasoline) in order to balance the exhaust gas purification rate of the engine 10 by the three-way catalyst CAT and the fuel consumption. The fuel injection amount may be controlled so that Further, when the accelerator operation with a relatively large operation amount is performed and the engine 10 is subjected to a high load (at the time of high load), such as when the vehicle is accelerated or started, the engine ECU 20 sets the air-fuel ratio of the engine 10 to the theoretical sky. The fuel injection amount may be controlled so that the fuel rich state is more than a predetermined value than the fuel ratio (fuel rich control). In addition, when the accelerator is turned off just before a downhill or just before the vehicle stops and the engine 10 is hardly loaded (at light load), control for cutting off the fuel supply to the engine 10 may be performed (fuel cut control). .

  The oxygen sensor 30 is a detection unit that is attached to the exhaust pipe EX of the engine 10 and detects the residual oxygen concentration contained in the exhaust gas of the engine 10. Specifically, a solid electrolyte (for example, zirconia) is arranged as a partition wall so as to touch both the exhaust gas and the atmosphere, and a platinum electrode is disposed on the exhaust gas (touching) side and the atmosphere (touching) side of the solid electrolyte. An oxygen sensor provided with may be used. In the oxygen sensor, depending on the difference in oxygen concentration between the exhaust gas side and the atmosphere side, the oxygen ions move from the higher oxygen concentration to the lower oxygen concentration in a direction that reduces the difference in oxygen concentration. Oxygen concentration in the exhaust gas can be detected by generating an electromotive force according to the difference. Further, the oxygen concentration in the exhaust gas greatly changes in the vicinity of the theoretical air-fuel ratio in relation to the air-fuel ratio of the engine 10. That is, since the residual oxygen concentration is high on the fuel lean side (the air / fuel ratio is greater than the theoretical air / fuel ratio) on the side where the air / fuel ratio of the engine 10 is the boundary of the stoichiometric air / fuel ratio, the difference from the atmospheric oxygen concentration is relatively small. A small electromotive force is generated. On the other hand, on the fuel rich side (the air-fuel ratio is smaller than the stoichiometric air-fuel ratio), since the residual oxygen concentration is low, the difference from the oxygen concentration in the atmosphere is large and a relatively large electromotive force is generated. When the air-fuel ratio of the engine 10 is near the stoichiometric air-fuel ratio, an electromotive force is generated between the fuel-rich side voltage and the fuel-lean side voltage. Thus, the oxygen sensor 30 detects whether the air-fuel ratio of the engine 10 is on the fuel-rich side, the fuel-lean side, or near the stoichiometric air-fuel ratio with respect to the stoichiometric air-fuel ratio. Can do.

  Based on the output voltage from the oxygen sensor 30, the engine ECU 20 determines whether the air-fuel ratio of the engine 10 is on the rich side, the lean side, or near the stoichiometric air-fuel ratio with respect to the stoichiometric air-fuel ratio. The determination value for determining is stored in advance in an internal memory or the like. Specifically, the rich voltage VR for determining whether or not the air-fuel ratio of the engine 10 is on the fuel rich side, and whether or not the air-fuel ratio of the engine 10 is on the fuel lean side is determined. A lean voltage is set in advance. Note that the rich voltage VR and the lean voltage VL are set as constant values in consideration of initial variation of the oxygen sensor 30 and aging degradation.

  Next, characteristic processing by the engine control apparatus 1 (engine ECU 20) according to the present embodiment, that is, processing for correcting the output voltage of the oxygen sensor 30 (output correction processing) will be described. More specifically, it is determined whether or not a deviation (offset) in output voltage has occurred among changes in the output characteristics of the oxygen sensor 30, and if there is a deviation in output voltage, the output voltage of the oxygen sensor 30 is determined. (Correction for offset of output voltage).

  FIG. 2 is a flowchart showing an example of output correction processing of the oxygen sensor 30 by the engine control device 1 (engine ECU 20). The flowchart may be executed every time the ignition switch of the vehicle is turned on (IG-ON).

  First, in steps S101 to S104, preprocessing for determining whether or not to correct the output of the oxygen sensor 30 is executed.

  In step S101, it is determined whether or not the fuel supply to the engine 10 is cut (fuel cut control). When the fuel cut control is not being performed, the determination process is repeated until the fuel cut control for the engine 10 is executed. When the fuel cut control is executed, the process proceeds to step S102.

  In step S102, the output value (lean side output voltage VLout) of the oxygen sensor 30 during the fuel cut control is stored in the internal memory or the like as the actual value of the lean voltage VL.

  In step S103, it is determined whether fuel rich control of the engine 10 is being executed. When the fuel rich control is not executed, the determination process is repeated until the fuel rich control of the engine 10 is executed. When the fuel rich control of the engine 10 is executed, the process proceeds to step S104.

  In step S104, the output value (rich side output voltage VRout) of the oxygen sensor 30 during the fuel rich control of the engine 10 is stored in the internal memory or the like as the actual value of the rich voltage VR.

  In this example, the lean side output voltage VLout as the actual value of the lean voltage VL is stored first, and then the rich side output voltage VRout as the actual value of the rich voltage VR is stored, but the order is reversed. But you can.

  Subsequently, in steps S105 to S107, it is specifically determined whether or not to correct the output of the oxygen sensor 30. That is, it is determined whether or not a deviation (offset) of the output voltage to be corrected has occurred.

  In step S105, it is determined whether or not the difference between the rich output voltage VRout and the lean output voltage VLout is equal to or greater than a predetermined value A. Note that the predetermined value A is the difference in the output voltage of the oxygen sensor 30 that is assumed when the air-fuel ratio of the engine 10 is on the fuel-rich side and the fuel-lean side with respect to the stoichiometric air-fuel ratio (the oxygen sensor 30 It may be set as the minimum value of (amplitude). If the determination condition is satisfied, the process proceeds to step S106. If the determination condition is not satisfied, the output of the oxygen sensor 30 is not corrected, and the current process ends. That is, when the difference between the actually measured rich side output voltage VRout and the lean side output voltage VLout is smaller than the assumed amplitude of the oxygen sensor 30, there is a possibility that an abnormality has occurred in the oxygen sensor 30, and the simple Output correction (correction for offset of output voltage) cannot be performed. Therefore, if the determination condition of this step is not satisfied, the output correction of the oxygen sensor 30 is not performed. If the determination condition of this step is satisfied, a shift in the output voltage to be corrected occurs in the oxygen sensor 30 in steps S106 and S107. It is determined whether or not.

  In step S106, the increments AR and AL of the rich voltage VR and the lean voltage VL (the increment AR of the rich output voltage VRout measured with respect to the preset rich voltage VR and the actual measurement with respect to the preset lean voltage VL). It is determined whether both of the increased lean side output voltage VLout (AL) are equal to or greater than a predetermined value B. The predetermined value B may be set as a value corresponding to the range of variation in the output voltage of the oxygen sensor 30. If the determination condition is satisfied, the process proceeds to step S107. If not satisfied, the output of the oxygen sensor 30 is not corrected and the current process is terminated. That is, when the increments AR and AL of the rich voltage VR and the lean voltage VL exceed the range of variation in the output voltage of the oxygen sensor 30 (is equal to or greater than a predetermined value B), the output characteristics of the oxygen sensor 30 to be corrected It can be determined that a change has occurred. On the other hand, when the increments AR and AL of the rich voltage VR and the lean voltage VL are within the variation range of the output voltage of the oxygen sensor 30 (smaller than the predetermined value B), the change in the output characteristic to be corrected to the output characteristic of the oxygen sensor 30 It can be determined that no has occurred.

  In step S107, it is determined whether or not the difference between the rich voltage VR and the lean voltage VL is equal to or less than a predetermined value C. If the determination condition is satisfied, the process proceeds to step S108. If the determination condition is not satisfied, the output of the oxygen sensor 30 is not corrected, and the current process ends. That is, when the increments of the rich voltage VR and the lean voltage VL are substantially equal (the difference is equal to or less than the predetermined value C), it can be determined that an offset has occurred in the output voltage of the oxygen sensor 30. On the other hand, when the increments of the rich voltage VR and the lean voltage VL are different (the difference is larger than the predetermined value C), the change in the output characteristics of the oxygen sensor 30 is not a simple output voltage shift (offset). Output correction of the sensor 30 (correction of output voltage deviation) is not performed.

  Note that the order in which the determinations in steps S105 to S107 are performed may be arbitrary.

  In step S108, the output correction of the oxygen sensor 30 is executed. Specifically, correction is performed by subtracting a value (= 1/2 · (AR + AL)) obtained by multiplying the sum of the increments AR and AL of the rich voltage VR and the lean voltage VL by 1/2 from the output of the oxygen sensor 30. That is, the average value of the increments AR and AL of the rich voltage VR and the lean voltage VL is calculated as the deviation amount (offset amount) of the output voltage of the oxygen sensor 30, and the deviation amount is subtracted from the output voltage of the oxygen sensor 30. Thus, the change in the output characteristics of the oxygen sensor 30 can be corrected. The correction is continuously performed while the vehicle is in the IG-ON state.

  As described above, the engine control apparatus 1 (engine ECU 20) according to the present embodiment determines whether or not there is a characteristic deviation (offset) to be corrected in the output voltage of the oxygen sensor 30, and the characteristic deviation occurs. If so, the output of the oxygen sensor 30 is corrected. Specifically, as the actual values of the rich voltage VR and the lean voltage VL, the output voltage (rich side output voltage VRout, lean side output voltage VLout) of the oxygen sensor 30 during fuel rich control and fuel cut control is stored in an internal memory or the like. Remember me. Then, based on the stored rich side output voltage VRout and lean side output voltage VLout, it is determined whether or not a deviation (offset) to be corrected has occurred in the output voltage of the oxygen sensor 30. That is, it is determined whether or not the increments AR and AL of the rich voltage VR and the lean voltage VL are both greater than or equal to the predetermined value B, and the difference between the increments of the rich voltage VR and the lean voltage VL is greater than or equal to the predetermined value C. To do. When the determination condition is satisfied, the average values of the increments AR and AL of the rich voltage VR and the lean voltage VL are calculated, and correction is performed to subtract the average value from the output voltage of the oxygen sensor 30. As a result, the engine ECU 20 can appropriately execute the air-fuel ratio control against a disturbance such as a deviation (offset) in the output voltage of the oxygen sensor 30.

  In addition, the engine control device 1 (engine ECU 20) determines that the difference between the actually measured rich-side output voltage VRout and the lean-side output voltage VLout is equal to or greater than the assumed amplitude (predetermined value A) of the oxygen sensor 30. The output of the oxygen sensor 30 is corrected. On the other hand, when the difference between the actually measured rich-side output voltage VRout and lean-side output voltage VLout is smaller than the assumed amplitude (predetermined value A) of the oxygen sensor 30, the output correction of the oxygen sensor 30 is not performed. That is, when there is a possibility that an abnormality has occurred in the oxygen sensor 30 (the amplitude of the oxygen sensor 30 has dropped below an assumed value), the measured rich-side output voltage VRout and lean-side output voltage VLout The output correction of the oxygen sensor 30 is not performed. Thereby, the case where the output voltage of the oxygen sensor 30 cannot be corrected appropriately, that is, the case where an abnormality occurs in the amplitude of the oxygen sensor 30, can be excluded from the output correction target of the oxygen sensor 30.

  As mentioned above, although the form for implementing this invention was explained in full detail, this invention is not limited to this specific embodiment, In the range of the summary of this invention described in the claim, various Can be modified or changed.

1 Engine control device 10 Engine (internal combustion engine)
20 Engine ECU
30 oxygen sensor A predetermined value (first predetermined value)
B Predetermined value (second predetermined value)
C predetermined value (third predetermined value)
CAT Three-way catalyst EX Exhaust pipe

Claims (1)

An output correction method for an oxygen sensor attached to an exhaust pipe of an internal combustion engine,
A lean voltage for determining whether or not the air-fuel ratio in the combustion chamber of the internal combustion engine is on the fuel lean side with respect to the stoichiometric air-fuel ratio, and the air-fuel ratio with respect to the stoichiometric air-fuel ratio, As the rich voltage for determining whether or not the fuel rich side is greater than or equal to a predetermined value, the output voltage of the oxygen sensor during fuel cut control of the internal combustion engine, and the output of the oxygen sensor during fuel rich control of the internal combustion engine A first step of storing an output voltage;
The difference between the rich voltage and the lean voltage is equal to or greater than a first predetermined value, and the rich voltage and the lean voltage are increased by a second predetermined value or more with respect to a preset rich voltage and lean voltage. And when the difference between the rich voltage and the increase in the lean voltage is equal to or smaller than a third predetermined value, a value obtained by multiplying the sum of the increase in the rich voltage and the lean voltage by 1/2. A second step of performing correction to subtract from the output voltage of the oxygen sensor,
Oxygen sensor output correction method.

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